A cohort of haemophilic patients who seroconverted to HIV-1 between October 1979 and July 1985 has been followed to 1 January 1992. The median age at initial seropositivity was 24 years with a range of 2-77 years. By January 1992, 38/111 (34%) had developed AIDS and 39/111 (35%) had died (four of liver failure including one hepatoma). Using Kaplan-Meier plots, the calculated progression to AIDS at 12 years is 45% (95% CI 31, 58): for age > 25 years 63% (95% CI 45, 82), age < 25 years 32% (95% CI 15, 48) P = 0.0001; CMV positive 68% (95% CI 48, 87) CMV -ve 20% (95% CI 8, 32) P = 0.0009. The 12-year progression rate to CD4 + 0.2 or AIDS is 66% (95% CI 55, 76). 21/34 (63%) of patients who are p24 antigen positive have developed AIDS compared to 17/77 (22%) who are p24 antigen negative (= 0.0001). 19/34 (56%) and 20/77 (23%) of those p24 positive and negative respectively have died (P = 0.007). Before antiviral and prophylactic treatment for asymptomatic patients there were nine AIDS cases in 3.84 years experience with CD4+ < 0.05 (1/0.43 years) and since treatment, 10 AIDS cases in 18.22 years (1/1.8 years). Age, CMV status and p24 remain strongly predictive of disease progression. Treatment appears to reduce the incidence of AIDS.