The aim of this study was to calculate the familial risk for prostate cancer (PC) for different family relationships. PC was studied in the Swedish Family-Cancer Database, updated in 1999 to cover individuals born after 1934 with their biological parents, totalling 9.6 million persons. Cancer data were obtained from the Swedish Cancer Registry from 1958 to 1996 and included 1035 PC cases amongst offspring. 188 families were identified where a father and a son had PC, giving a familial standardised incidence ratio (SIR) of 2.44 (2.10-2.80). The proportion of familial cancers was 18.2% amongst all PC amongst all PC amongst sons. There were only 5 pairs of affected brothers, of which 3 had an affected father. Age of onset modified familial risks modestly; the highest SIR of 4.43 (1.40-9.17) was for sons diagnosed before 50 years of age when the father was diagnosed before 65 years of age. When analysed across sites, an association of PC in one generation and stomach, liver and skin cancer and myeloma in another generation was observed. The link was most consistent for skin cancer. No maternal site was associated with a son's PC, although the SIR of breast cancer was 1.22 (0.95-1.53). No increased risk of malignancy was observed in wives of affected men excluding any shared environmental effect for PC and female cancers.