European data on transfusion-associated (TA) AIDS cases reported by December 31, 1989 have been analyzed using both parametric and nonparametric methods. Parametric estimates of the median incubation period of TA AIDS in adults vary from 6.5 to 11 years according to the type of distribution assumed (Weibull or gamma) and the latest year of diagnosis included (1987 or 1988). The latter finding may reflect a lengthening of the incubation period due to increasing treatment of HIV-infected patients prior to the development of AIDS. It is predicted that, by the end of 1991, between 2,000 and 3,000 cases of AIDS will have been diagnosed in Europe among adults infected by transfusion between 1978 and 1985 (when systematic screening of donated blood was introduced in most western countries). It is not possible, however, to predict how many further cases may arise among those transfused more recently in countries in which screening was introduced at a later date.