This subgroup analysis assessing secondary prophylaxis for Pneumocystis carinii pneumonia (PCP) describes a multicenter, open-labeled, randomized, controlled trial evaluating the discontinuation of PCP prophylaxis. The main inclusion criterion was a history of PCP and an increase in the CD4 cell count to >200 cells/microL associated with receipt of highly active antiretroviral therapy for >or=3 months. The primary end point was the development of definitive or presumptive PCP. A total of 146 patients were enrolled (77 in the treatment discontinuation arm). After >2 years, 1 definitive and 1 presumptive case of PCP were observed, both of which occurred in patients who discontinued therapy. In most patients, secondary prophylaxis for PCP can be safely discontinued after potent antiretroviral therapy is initiated, but the threshold of >200 CD4 cells/microL may not be considered absolutely safe. Patients who present with symptoms after discontinuation of secondary prophylaxis should be evaluated for PCP despite high CD4 count and complete virus suppression.