We studied familial risks in invasive and in situ cutaneous melanoma by comparing the occurrence of melanoma, or discordant cancer, between parents and offspring, and between siblings, based on the Swedish Family Cancer Database of over 10 million individuals. Offspring were 0-66 y of age. Cancers were obtained from the Swedish Cancer Registry from 1961 to 1998. The study was based on 24,818 invasive and 5510 in situ cases of melanoma. Standardized incidence ratios were calculated for familial risk. The standardized incidence ratios for offspring was 2.40 (95% confidence intervals: 2.10-2.72) when only the parent had melanoma and it was 2.98 (95% confidence intervals: 2.54-3.47) when only a sibling was affected; when both a parent and a sibling were affected the standardized incidence ratios was 8.92 (95% confidence intervals: 4.25-15.31). The respective population attributable risks were 1.38, 1.20, and 0.10%. The familial risk showed a clear age dependence and somewhat higher risk in in situ melanoma than in the invasive counterpart. The highest standardized incidence ratio of 61.78 (5.82-227.19) was noted for offspring whose parent had multiple melanomas. Superficially spreading melanoma showed the highest familial risk both among invasive and in situ tumors. Melanoma associated with breast, nervous system, and skin cancers, and in situ melanoma possibly also with connective tissue and thyroid tumors and multiple myeloma.