The campaign, "The Bronx Knows," is aimed at reaching 250,000 Bronx adults who have never been tested, the agency said. The Health Department said Bronx residents will be able to go to any one of 40 locations throughout the borough for fast, free, reliable testing.

Bronx residents account for nearly one-fourth of New York City's HIV infections and one-third of AIDS deaths each year. More than a quarter of Bronx residents who tested positive for HIV in 2006 were already sick with AIDS by the time they learned they had HIV.

The Health Department said the individuals had likely been infected for nearly a decade.

"The Bronx has the opportunity to lead the city in the fight against HIV/AIDS by being the first borough to have all residents tested," Health Commissioner Dr. Thomas R. Frieden said in a statement. "This effort will set a model not only for the city but for the whole country."