Twenty-one immunodeficiency virus 1 (HIV 1)-positive hemophilic patients were treated with Azidothymidine (AZT) for symptomatic HIV infection. The median observation period was 20.5 months. At 25 months the probability of survival was 82%, the probability of progression of disease from CDC III or IV C2 to IV C1 (AIDS) was 20% in patients on continuous AZT treatment and 50% in patients with interruption of treatment. Three patients developed severe leukopenia and 3 patients severe anemia during AZT treatment. In 1 patient a dose-dependent striking increase of transaminases during AZT treatment was observed. In 7 patients treatment was interrupted, in 1 patient because of anemia, in 1 because of pruritus and in 5 patients because of non-compliance. No significant changes in the consumption of clotting factor concentrates and number of bleeding episodes before and during AZT treatment were noted. We conclude, that both hematological and non-hematological side effects of AZT in HIV 1-infected hemophilic patients are comparable to those seen in other risk groups. AZT does not increase the bleeding tendency in this patient group.