Between 1943 and 1982, 5,140 new cases of testicular cancer were diagnosed in Denmark. The age-standardized incidence rate more than doubled in the period. Striking variations is seen in the age-relationship over time with a four-fold increase in incidence for men aged 15-24 years while no increment was observed for those above 65 years of age. The increase with time in the risk could be accounted for by a cohort effect. The mortality rate did not parallel the incidence rate and a 50% decrease in mortality rate appeared in the period 1978-1982. Introduction of combination chemotherapy including cis-platinum is one of the main factors responsible for this beneficial development. The observed pattern of diverging trends in incidence and mortality of testicular cancer implies that mortality rates do not reflect the incidence and will accordingly be unsuited as a basis for aetiological considerations based on trends. The brisk increase in the risk of testicular cancer, especially among young men is in accordance with trends in other western countries, and prompts an enforced search for suspected or new risk factors.