Susan Posen readily admits she was not born a fashionista. She didn’t grow up thumbing through Vogue or dreaming of dresses. On the other hand, as a young lawyer, she did make a fashion statement by refusing to wear those mannish suits with little bow ties so favored by female up-and-comers in the 1980s. So as not to scare her corporate clients, she wore conservative dresses instead. Nothing flashy, but still, it was a statement.

Notwithstanding this indifference, today Ms. Posen is the CEO of Outspoke, one of the country’s most exciting young fashion enterprises. It just happens that the talent behind this rapidly growing outfit is her son, Zac, who has grown and matured creatively and is now all of 25 years old. Of course he needs his mother!

Ms. Posen is a New Yorker by inclination and birth. She is married to artist Stephen Posen, who in her view, is the source for the wildly creative accomplishments of their son, Zac, and their daughter, Alexandra, who is the creative director of Outspoke.

Ms. Posen graduated from Sarah Lawrence and received her law degree from Brooklyn Law School. From there she moved to Strook & Strook & Lavan, where in due course she made partner. Like many women breaking the glass ceiling in the 1980s, Ms. Posen often faced the conflicting needs of family and career. Her daughter was born before she made partner. She and her husband waited eight years to have Zac; the demands of her job were pressing.

Ms. Posen practiced merger and acquisitions law, and specialized in venture capital activities. By 2000 she decided the time had come to relinquish her hard-won partnership. Her partners were agog. It simply wasn’t done. Nonetheless, she moved on and quickly joined a budding enterprise, taking full advantage of her skill set.

A friend had started a venture capital firm called Diva, catering to female entrepreneurs. Just as this promising group was about to launch its first fund, the bottom fell out of the markets. For the record, the top fell out, too. Old firms and new fell by the wayside, and Diva’s fund was stillborn.

Serendipitously, about this time Zac Posen returned from the renowned design school Central St. Martins in London, a training ground for many brilliant fashion names such as John Galliano and Alexander McQueen. He announced that he wanted to start a fashion house. His vision was clear: His line would be defined by unparalleled quality, finishing, and construction. It would be, in this country, unique.

Zac first convinced his sister, an aspiring artist, and then his mother to join him in his quest. Ms. Posen imagined that her contribution would be to review the occasional contract. In the end, Alexandra and Zac oversee the creative process; Ms. Posen does everything else. It’s not as though Zac has no interest in finance. On the contrary, he says, “I love the business side. Everything here is collaborative.”

Many start-ups begin in the living room. Such was the case for Outspoke. Poor Mr. Posen, who was accustomed to painting in the family’s SoHo loft during the day, suddenly found himself surrounded by fabric bolts, mannequins, and bedlam.

The timing could not have been worse. The business was officially formed on September 1, 2001. Stunned by the terrorist attacks, the family nonetheless was determined to proceed and arranged to hold its first show in February 2002, at a defunct synagogue now called Angel Orensanz. The collection featured 25 “looks” and models of all shapes and sizes. Zac was making a statement: All kinds of women are beautiful. The enthusiastic front row featured Anna Wintour and other tastemakers; Outspoke was off and running.

Of course, this reception was not without prelude. Ever since the eighth grade, Zac had evinced an interest in learning to sew, and had started making dresses for his girlfriends. He went to St. Ann’s in Brooklyn, where according to his mother, he experienced a “creative explosion” and had “the happiest possible high school experience.” He won awards for writing and art, and even excelled in math – especially geometry, which perhaps explains his mastery of forms and shapes.

Early on, he designed a nude velvet dress with a fuschia lining for his young artist friend Stella Schnabel, daughter of Julian Schnabel. She wore it in Italy, and it caught the eye of Gianni Versace. Bit by bit, Zac’s reputation grew, and with it the company.

Today the firm employs 30 people and has revenues between $5 million and $10 million. Each collection has won rave reviews and increased orders from retailers. The company has been choosy about its vendors, selling only to top-line stores such as Neiman Marcus and Saks. About 40% of revenues today come from Europe – unusual for a young American brand.

Outspoke also watches carefully over the production of its line; to that end almost all the garments are produced in the New York area, though Ms. Posen says this is a challenge. Over time the supporting infrastructure for the garment industry in New York has melted away. As most firms grow, they eventually have to source abroad.

In 2004, Zac asked Sean Combs to provide music for one of his shows. The two became friendly, and before long the young designer entered a 50-50 joint venture with Mr. Combs, who supplied much-needed capital in return for his stake. It has been a valuable relationship, Ms. Posen says. Zac has retained total creative autonomy and has received some valuable advice and backing.

What’s next? The firm has launched a line of shoes and bags, and each new collection takes the company to a new level. Ms. Posen is confronting the challenges of building a company – dealing with the kinds of issues she consulted on as a lawyer. “I find myself a cost accountant,” she says with horror. “More and more we have scheduled meetings. Lines of reporting are becoming necessary.” Is it ever tough working with her children? “The tensions that exist are not familial,” she says, “but rather between creative and financial.” For example, occasionally it is her job to point out that a fabric particularly admired by her children is lovely, but just too costly.

Ms. Posen knows her limitations. Her views on design are generally not sought and, she concedes, not usually on the mark. However, her business sense is key to Outspoke’s success. Her ambition? She shares her son’s dream “to build a luxury global brand.” By any measure, they are well on their way.