Forty-three strains of adenovirus type 3 isolated from patients in Norway between 1970 and 1991 were analyzed with four restriction endonucleases. Bg1 II was the most discriminative enzyme. Five genotypes were identified and one of these has not been described before (Ad3a12). During both the epidemics in this period, new genotypes were introduced into the population. The same genotypes were identified in Norway as have previously been found in the northern parts of Europe, America and the Soviet Union.