To assess the association between adult body size and germ-cell testicular cancer risk and to understand whether this association is independent from perinatal characteristics, a nested case-control study was conducted. Three hundred and seventy-one patients with testicular cancer, registered in the Swedish Cancer Registry between 1958 and 1996 and aged 20-54 years at diagnosis, and 1238 individually matched controls were identified. Information on adult body size at age 18 years was obtained for all subjects through the Military Service Conscription Register, whereas perinatal information was obtained through birth records at the subjects' respective maternity wards. Height was positively associated with testicular cancer risk, and the association persisted after taking into account perinatal characteristics. The adjusted odds ratio (OR) was 1.55 [95% confidence interval (CI), 1.10-2.17] for the third tertile of height as compared with the first. No association between the risk for testicular cancer and body mass index was found. Long duration of gestation was negatively associated with testicular cancer risk [OR = 0.64 (95% CI, 0.45-0.91), post-term compared with term], whereas high birth weight appeared to increase the risk [OR = 1.35 (95% CI, 0.99-1.85)]. In conclusion, adult height and perinatal factors acted independently, suggesting that both the fetal life and the childhood and adolescence periods are windows of susceptibility to exposures that influence the risk for testicular cancer.