An individually matched case-control study of testis cancer in 131 men under age 40 was counducted to investigate antecedent risk factors including events during prenatal life. Ten patients were born with an undescended testis compared to only two controls (p = 0.02), a previously reported risk factor. Two new risk factors were uncovered: six patient-mothers received hormones during the Index pregnancy compared to only one control-mother, and eight patient-mothers and two control-mothers reported excessive nausea as a complication of the index pregnancy. A hypothesis linking these three factors is presented: viz. that a major risk factor for testis cancer is a relative excess of certain hormones (in particular estrogen) at the time of differentiation of the testes.