Two types of autosomal dominant retinitis pigmentosa (RP) are identified on the basis of perimetric measures of rod sensitivity relative to cone sensitivity. Type 1 dominant RP patients are characterized by an early diffuse loss of rod sensitivity with a later loss of cone sensitivity and by childhood onset of night blindness. Type 2 dominant RP patients are characterized by a regionalized and combined loss of rod and cone sensitivity with adulthood onset of nightblindness. Comparisons of losses in the photopic and scotopic electroretinogram amplitudes corroborate the psychophysical results. Clinical findings are similar for the two dominant RP subtypes, however, there are differences in natural history.