To assess the magnitude of the AIDS epidemic in the Italian adolescent (13-19 years) and young adult (20-24 years) age groups, data on AIDS cases notified to the AIDS Operational Centre as of 31 March 1990 were used. Of the 6068 reported AIDS cases, 0.7% occurred among adolescents and 15.7% among young adults. Among adolescents most cases were haemophiliacs (45.4%), while among young adults, drug use was the most frequently reported mode of transmission (87.5%). Females were more likely than males to contract the disease through the heterosexual contact in both the adolescent (20.0% vs 0%) and in young adult (15.1% vs 0.7%) age groups. Among young adults a geographical trend was present with a decrease in case rates from north to south, while for adolescents the rates were higher in northern and southern than in central Italy. If the incidence of AIDS is to be reduced in Italy, further efforts should be made to target the adolescent age group, since many of the young adult cases are likely to have resulted from HIV infection during adolescence.