435 hemophiliacs are usually being attended in the La Paz hemophilia Center (Madrid, Spain). 257 (59%) of these patients have been infected by the human immunodeficiency virus (HIV-1) because of human plasma derivate substitution therapy. The infection has been more frequent among the severely affected patients and among the most treated patients. 82% of the infected patients are between 14 and 40 years old. By December 1991, 95 (37%) of 257 seropositive patients have developed full-blown AIDS. The most frequent opportunistic infection they had suffered was esophageal can-didiasis. Looking for an evolution marker, we can point that the patients older than 35 years with CD4 levels below 200/mm3 had the worst prognosis. There was no difference in the evolution among the patients aged below 17 and those aged between 17 and 35 years. The amount of concentrate used between 1980 and 1984 did not hold any relation to the evolution. 49 patients (51%) of the 95 suffering from AIDS had died by December 1991. The evolution to the death was unrelated to the patient age, CD4 lymphocyte levels, and amount of substitution therapy. In our opinion, the most valuable marker could be the kind of opportunistic infection or tumor the patient suffers from. Finally, Retrovir has demonstrated to be useful in increasing the survival rate of the patients, but after 36 months of treatment, only 33% of those AIDS patients who began taking it remained alive. Retrovir was also used in asymptomatic patients, and during an average period of time of 15 months, a lesser bone marrow toxicity and a stabilization in CD4 lymphocyte levels could be observed, but this was unable to modify the disease progression in those patients who presented circulating p24 antigen.