John Kasye was new to New York when he developed a hacking cough and a fever one weekend in mid-March. Opposed to the idea of visiting an emergency room, the 39-year-old did what an increasing number of patients do: He logged on to the Internet and typed the words “New York City” and “doctor” into a search engine.

Immediately, Mr. Kasye found ZocDoc.com, a new Web site that allows patients to locate doctors and schedule same-day appointments online. In Mr. Kasye’s case, he booked the appointment at 9:30 a.m. on a Monday morning and by 10:15 a.m. he was in an examination room, where he was diagnosed quickly with bronchitis. “That’s pretty good for the Internet, right?” he said.

As patients turn to the Internet for health-related information, the New York City-based ZocDoc says it is making finding a physician as easy as locating a good restaurant on OpenTable.com or ordering groceries from the delivery company Fresh Direct. With a list of more than 100 practitioners in Manhattan and Brooklyn, the company distinguishes itself from other physician directories by vetting doctors through background checks and patient reviews.

The co-founder and CEO of the company, Cyrus Massoumi, said the idea for the site came to him during a business trip, when he suffered a ruptured eardrum during the airplane’s descent into New York. “It took me four days before I could get a doctor’s appointment,” he said, explaining that he preferred to see an ear, nose, and throat specialist and that he was wary about going to the emergency room. “Every time I’ve ever been in the emergency room, it’s been a very hellish experience,” he said.

ZocDoc launched in the fall of 2007 with a catalog of nearly 15 dentists in Manhattan. In February, it added a roster of several dozen internists in Manhattan and Brooklyn. “Primary care is a no-brainer,” Mr. Massoumi said. “It’s in such high demand and people need it.”

In the coming months, Mr. Massoumi said ZocDoc plans to add other medical specialists such as dermatologists to its listing. So far, more than 60 practitioners have added their names to a waiting list for the existing specialties. The site is free for patients, but doctors pay a transaction fee if they book a new patient through the site.

In addition to helping patients narrow their choice of doctors, ZocDoc’s founders said they are capitalizing on a push by policymakers to discourage patients from visiting costly emergency rooms. “It’s a big challenge both for the hospital to operate these emergency rooms and for the doctors,” the company’s chief operating officer, Dr. Oliver Kharraz, said.

Mr. Massoumi said if a patient needs emergency care, they should call 911. “We’re not trying to replace that,” he said. But the site can replace the emergency room if a patient is visiting the hospital for lack of a better option, he said.

Among doctors, some who are listed on ZocDoc said the site is an effective marketing tool. One physician who has been in private practice on the Upper West Side for two years, Dr. Martin Malachovsky, said ZocDoc doubled the number of patients in his small practice to include nearly 500 patients, up from 250. “These days, everyone just goes to Yahoo or Google,” he said, describing the appeal of Internet marketing.

Still, he echoed a concern voiced by some doctors that a bad patient review could sabotage his practice. “A couple of bad reviews, it would kill you,” he said.

For Dr. Malachovsky, that fear has motivated him to improve the service and attentiveness he thinks patients want. “It is subjective, but you know if someone waited too long or you were rude to him, you will read about it,” he said.

In the case of Mr. Kasye, who had recently moved to New York from Pennsylvania, the site was one method he used to scrutinize his doctor, a physician affiliated with NYU Langone Medical Center. Mr. Kasye said he chose the doctor after evaluating his educational background, looking at how long the doctor had been in practice, reading reviews written by other patients, and scouring the Internet for any other mentions of the physician. “You can’t hide from the Internet,” Mr. Kasye said.