ObjectiveTo determine the safety and efficacy of 100mg dapsone three times weekly for Pneumocystis carinii pneumonia (PCP) prophylaxis in HIV-infected, trimethoprim-sulfamethoxazole (TMP-SMX)-intolerant patients.DesignRetrospective chart review of patients followed-up to 22 May 1992.SettingInfectious diseases outpatient clinic of a tertiary care center in suburban New York City.PatientsTwenty-three HIV-infected patients requiring PCP prophylaxis with documented intolerance to TMP-SMX.Main outcome measuresPatients were followed clinically and with laboratory testing at approximately monthly intervals.ResultsDapsone was discontinued in nine (39%) patients because of adverse reactions. All reactions occurred within the first 2 months of treatment. Two (14%) of the remaining 14 patients developed histologically proven PCP over 126 patient-months of follow-up.ConclusionApproximately 40% of TMP-SMX-intolerant HIV-infected individuals are also intolerant of dapsone. Prophylaxis failures may be expected on a dose regimen of 100mg dapsone three times weekly. More experience with other dose regimens and alternative agents is needed.