Prostate cancer is the most commonly diagnosed cancer in men, but rates around the world vary greatly. Americans have the highest incidence rates in the world, 4 to 5 times those of Spain. The hypothesis of this thesis was that vitamin D metabolism is a factor in prostate cancer development and the aim was to examine differences in factors that modulate vitamin D metabolism between the US and Spain, specifically sunlight exposure and vitamin D receptor (VDR) polymorphisms. Through a search of papers that examined sunlight exposure and prevalence of VDR polymorphisms, we found that Spain had more ultraviolet exposure than the United States, but there was little difference in proportions of VDR polymorphisms between the two populations. TaqI, BsmI, and FokI polymorphisms of the VDR were studied. Proportions of TaqI and FokI were found to be equivalent between the two populations. The rates of BsmI polymorphisms were found to be statistically different, but the United States, not Spain, has higher proportions of the protective allele. With no apparent rate differences in the VDR polymorphisms these do not help explain the different prostate cancer rates. However, the increased sun exposure in Spain may allow more vitamin D production which could be a contributing factor for Spain having lower prostate cancer incidence rates.