A “horrific plague” of cockroaches infests the fabled Ansonia condominium on the Upper West Side, according to long-time residents, and regardless of whether roaches may infest the city, they say they have it the worst.

A lawsuit filed yesterday in state Supreme Court in Manhattan says there are cockroaches “in an unbearable volume” in the building’s hallways and within apartments every day, according to an 11-year resident and attorney, Alan Arkin, who filed the suit against the managing agent, Sirius.

“A cockroach once in a while is to be expected, this is New York, but to have 20 or 30 in your apartment on a given night, I’m not living in squalor,” Mr. Arkin said.

He added: “It’s a great building and this is an unfortunate situation.”

The suit seeks unspecified damages, and Mr. Arkin said other residents in the building may file similar complaints soon.

Mr. Arkin has filed formal complaints with his building and requested extermination services, according to the suit.

Sirius did provide some exterminating services in the building and in his apartment, but Mr. Arkin charges in the suit that the work was “inadequate.”

Calls and e-mail messages to Sirius were not returned yesterday evening.