The descriptive epidemiology of testicular cancer in Denmark shows that the incidence of both seminoma and non-seminoma has increased gradually since the 1940s to the present. The age-incidence pattern has remained unchanged, and is the same in the Nordic countries despite variation in the overall incidence level. Men born during the early 1940s have a lower risk in all age groups than expected from the overall trend in incidence. These observations support the idea that the occurrence of testicular cancer (both seminoma and non-seminoma) is determined early in life, and most probably before birth. Once the carcinogenic process is established, the age of occurrence of cancer or the histological type of the cancer does not seem to depend upon external factors.