The present case-control study was undertaken to investigate the association between exposure to maternal hormones and risk of testicular germ-cell cancer by histologic subgroups. Cases were males, aged 16 to 59 years, diagnosed with testicular germ-cell cancer in Ontario between 1987 and 1989. Histologic review was performed on all eligible cases for the purpose of categorizing cases as seminoma or nonseminoma (the latter classified 2 ways, with and without tumors containing seminoma). Risk factor data were collected on 502 cases, 346 case mothers, 975 age-matched controls, and 522 control mothers. Exogenous hormone exposure was associated with elevated risk (OR โซุโฌ 4.9, 95% CI 1.7-13.9). Several additional risk factors were associated with risk of testicular cancer: bleeding and threatened miscarriage (OR โซุโฌ 0.6, 95% CI 0.3-1.0), maternal cigarette smoking (12ุ cigarettes/day OR โซุโฌ 0.6, 95% CI 0.4 -1.0). pre-term birth (OR โซุโฌ 1.6, 95% CI 1.0 -2.5), and treatment for undescended testicle (OR โซุโฌ 8.0, 95% CI 3.2-20.0). First births were associated with elevated risk (OR โซุโฌ 1.7, 95% CI 1.0 -2.8) among mothers below the age of 24 years at conception. There was little evidence that risk factors differed by histologic subgroup. We found evidence that exposure to maternal hormones, particularly estrogens, is associated with testicular germ-cell cancer risk. Not only does exposure to elevated levels (exogenous hormone use, pre-term birth, and first births among young mothers) increase risk but also exposure to relatively lower levels (heavy cigarette consumption and, perhaps, bleeding and threatened miscarriage) may decrease cancer risk.