Increased body mass index (BMI) is claimed to be a complication among survivors of testicular cancer (TCSs), especially after receiving cisplatin-based chemotherapy. This study compares changes in BMI (kg m(-2)) in TCSs with those observed in age-matched men from the population (controls). Associations between treatment, age and potential BMI changes were sought. In 1999, a survey was performed at the NRH of 444 unilaterally orchiectomised TCSs treated from 1980 to 1990. BMI at survey was recorded in each TCS. Information on principal treatment (surgery only: SURG; radiotherapy only: RAD; chemotherapy +/- surgery or radiotherapy: CHEM+/-) and pretreatment BMI was retrieved from the medical records. The age-matched controls had BMI measurements from population surveys from 1985 and 1996. The annual BMI increase was calculated based on the difference in the two BMI measurements divided by observation time. TCSs displayed a lower pretreatment mean BMI than the controls, whereas no difference was found post-treatment. However, the annual BMI increase in TCSs exceeded that of the controls (0.19 vs 0.15, P=1.4 x 10(-7)). The SURG and CHEM+/- groups showed the greatest annual BMI increase. The multiple regression analysis showed that young TC patients who received chemotherapy displayed an excessive annual BMI increase. Oncologists and young TCSs should be aware of the risk of excessive BMI increase, in particular, after the use of chemotherapy.