The aim was to determine the prevalence of HIV infection and risk factors for HIV infection in various population subgroups in Ethiopia. Serum panels from blood donors (n = 2610), from various population subgroups in Ethiopia were tested for anti-HIV-1/2 by ELISA. All ELISA repeatedly reactive samples were subjected for confirmation by immunoblot (IB) and anti-HIV-1 and anti-HIV-2 specific ELISAs. 155/2610 (5·9%) blood donors were HIV-1 infected. Of pregnant women, 84/797 (10·5%) were HIV-1 infected, and 1/797 (0·1%) was HIV-2 infected. 1/240 (0·4%) individuals from the rural population were HIV-1 infected. 198/480 (41·3%) female attendees, and 106/419 (25·3%) male attendees at sexual transmitted disease (STD) clinics were HIV-1 infected. One (0·2%) male, and 2 (0·4%) female STD patients were infected with both HIV-1 and HIV-2. It was concluded that the prevalence of HIV-1 infection varied from 0·4% among urban residents to 25·3–41·3% among STD attendees. There is a low prevalence of HIV-2 present in Ethiopian subjects. Risky sexual behaviour is significantly associated with HIV-infection in Ethiopia.