DURING 1977-91, 6,278 males diagnosed with haemophilia were living in the UK. During 1979-86, 1,227 were infected with the human immunodeficiency virus (HIV-1) as a result of transfusion therapy (median estimated seroconversion date, October 1982). Among 2,448 with severe haemophilia, the annual death rate was stable at 8 per 1,000 during 1977-84; during 1985-92 death rates remained at 8 per 1,000 among HIV-seronegative patients but rose steeply in seropositive patients, reaching 81 per 1,000 in 1991-92. Among 3,830 with mild or moderate haemophilia, the pattern was similar, with an initial death rate of 4 per 1,000 in 1977-84, rising to 85 per 1,000 in 1991-92 in seropositive patients. During 1985-92, there were 403 deaths in HIV seropositive patients, whereas 60 would have been predicted from rates in seronegatives, suggesting that 85% of the deaths in seropositive patients were due to HIV infection. Most of the excess deaths were certified as due to AIDS or to conditions recognized as being associated with AIDS.