To determine whether HIV-1-seropositive cigarette smokers progress more rapidly to AIDS than HIV-1-seropositive non-smokers. The genitourinary medicine outpatient department of St Mary's Hospital, London, which is a London University teaching hospital (tertiary care centre). Case series of 84 individuals with AIDS who provided accurate details of their smoking habits before their AIDS-defining diagnosis. Progression time to AIDS in relation to smoking habit. Progression time to AIDS (all diagnoses) was significantly reduced in HIV-1-seropositive smokers: median time to AIDS was 8.17 months for smokers (n = 43) and 14.50 months for non-smokers (n = 41) (P = 0.003). Smokers developed Pneumocystis carinii pneumonia (PCP) more rapidly than non-smokers, with a median time to PCP of 9.0 months, compared with 16.0 months for non-smokers (P = 0.002). Smoking had no significant effect on progression time to AIDS when not due to PCP. Cigarette smoking by HIV-1-seropositive individuals is associated with a more rapid development of AIDS and should be discouraged.