A total of 173 patients, from 124 families, with retinitis pigmentosa were evaluated for the presence of various forms of genetic transmission. Of the 124 pedigrees, it was evident that some form of genetic transmission had occurred in 59 (48%). In 65 families (52%), the proband was the only known affected family member (isolated case). In those families with know genetic transmission, 17% (10 patients) were X-linked recessive, 39% (23 patients) were either probable or certain autosomal dominant, 41% (24 patients) were certain or probable autosomal recessive, and 3% (2 patients) were of a genetic type that could not be determined with certainty. These findings are, to my knowledge, the first published series from the United States to indicate that the X-linked recessive form of retinitis pigmentosa is a more prevalent genetic trait than has been emphasized previously.