OBJECTIVE To use a statewide population-based genealogic database to evaluate the relationship between Parkinson disease (PD) and cancer subtypes. DESIGN Using a computerized genealogy for the Utah pioneers and their descendants linked to a statewide cancer registry and statewide death certificates, we estimated relative risks for cancer in individuals with PD listed on their death certificate, and in their first-degree, second-degree, and third-degree relatives. SETTING Utah Cancer Registry. PARTICIPANTS Approximately 2.3 million individuals in the Utah genealogic resource, including death certificates of 2998 individuals with PD listed as a cause of death from 1904 to 2008 and information on 100 817 individuals with a cancer diagnosis in the Utah Cancer Registry. RESULTS Melanoma and prostate cancer were the only cancers observed in significant excess among PD cases; colorectal, lung, pancreas, and stomach cancers were observed in deficit. A significantly increased risk for prostate cancer was observed in the PD population as well as among their relatives. A reciprocal significantly increased risk for PD was also found in the 22 147 prostate cancer cases and their relatives. A significantly elevated risk for melanoma was found in the Utah PD population as well as in their relatives. A reciprocal significantly increased relative risk for PD was found in 7841 Utah melanoma cases and their relatives. CONCLUSIONS Our study identified a novel association between PD and prostate cancer, which extended to first-degree, second-degree, and third-degree relatives. We also confirmed the reported risk association for melanoma in patients with PD; we extended the finding to include a significantly increased risk in relatives. These results strongly support a genetic link. This conclusion is further strengthened by observation of the reciprocal relationship, an increased risk for PD in relatives of individuals with melanoma or prostate cancer.