In a nation-wide study we utilized all available sources to characterize the prevalence rates of retinitis pigmentosa. 1301 persons, 715 males and 586 females, were identified, with a diagnosis of retinitis pigmentosa or some other tapetoretinal dystrophy, and living in Denmark per January 1, 1988. The corresponding completeness corrected prevalence rate of retinitis pigmentosa was 1:3026. All cases were classified as 'certain', 'probable', or 'possible'. The age specific prevalence rates increased until 40-50 years, reaching a level of 35-40 male cases per 100,000 and 25-30 female cases per 100,000. Age specific prevalence rates were standardized to the WHO World Standard Population and compared to rates reported from Britain and The United States. World standardized prevalence rate for males was 25.29 per 100,000 and for females 19.31 per 100,000. The preponderance of males was highly statistically significant, (P less than 0.01).