The Swedish Family-Cancer Database was used to assess familial cancer risks in first-degree relatives and the risks of second primary cancers in testicular cancer patients by the histological type of their testicular cancers. Standardised incidence ratios (SIRs) were employed to estimate cancer risks. Among 4650 patients, 1.3% were familial testicular cancer. Seminomas showed a 10 years later median age of onset than teratomas (30 versus 40 years). The familial risks of testicular cancer were 3.8 for fathers, 8.3 for brothers and 3.9 for sons; they were similar for the two histologies. The fraternal risks were elevated 2- to 2.8-fold for pure histologies compared with the mixed histologies. Significantly increased risks for subsequent cancers were observed in the stomach, pancreas, testis, kidney, bladder, thyroid and connective and lymphatic tissues in the patients. Our data support the contention that genetic predisposition is one of the major contributors to familial and multiple testicular cancers.