Roosevelt Island’s first market-rate condominiums are in hot demand, with prices increasing in some cases by more than 80% in their first four months on the market.

Riverwalk Place, a luxury development in the Southtown area across from Midtown Manhattan, has seen the price of its three-bedroom units jump 81% to $1.225 million from $675,000 when the units went on sale in October, according to prices listed on the development’s Web site. Studios have nearly doubled to $405,000 from $220,000, while one-bedroom condos have risen to $540,000 from $290,000, and two bedroom units are up to $700,000 from $480,000. While these price hikes are steep, they may be rising in part because units on the lower floors are sold when the apartments first hit the market, with premium apartments going on the market more recently.

Riverwalk Place, which is scheduled to open for its first tenants early next year, will offer residents a 24-hour at tended lobby with marble and wood paneling, a fitness center, an adjacent garden terrace, a roof deck, and an entertainment suite. There is also a children’s playroom, a bicycle room, an ATM, and storage lockers.

While The Related Companies, which is developing the project with the Hudson Companies, would not comment on the development, the company’s Web site said the development “was conceived from the very beginning as a full-service luxury high-rise, faithful to the standards of Manhattan’s most desirable residences.”

Riverwalk Place will soon be joined by a second market-rate development at the nearby Octagon, a 13-story rental building with 500 units developed by Bruce Redman Becker. Built from what is left of the New York City Lunatic Asylum, the development will also include some fixed-income units, according to the vice president of the Roosevelt Island Operating Company, John Melia.

In Southtown, where Riverwalk Place is going up, there are two other developments by The Related Companies that have been built for the medical staff of Memorial Sloan-Kettering and Cornell Medical College. Southtown has another six parcels of land ready to be developed that have not yet been purchased by developers, Mr. Melia said.

“The six remaining plots have not been spoken for, and we are not in any active negotiations with developers to build on the land now,” Mr. Melia said.

The Roosevelt Island Operating Corporation, or RIOC as it is known, is a public benefit corporation established by New York State in 1984 to manage and develop the 147-acre island in the East River.

“It is very complex to develop on Roosevelt Island because the city leases the land to us so that we can develop it until 2069, at which point it reverts back to the city. Until that time, we allow developers to build on the island for a fee,” Mr. Melia said. “By all accounts, it is bizarre, and we have had a difficult time getting developers to build here. With such a strong real estate market, however, things might be looking up.”