There have been a number of histopathologic studies of retinas that were taken post mortem from patients with retinitis pigmentosa (RP), but few have addressed the question of transneuronal degeneration of ganglion cells secondary to photoreceptor death. We studied sectioned maculae that were obtained from 41 patients with different genetic forms of RP: autosomal dominant (n = 11); X-linked (n = 9); and simplex (n = 21). We also studied sectioned maculae that were taken from 20 age-matched normal subjects. We counted cell bodies in the photoreceptor and ganglion cell layers at 100-microns (0.35 degrees) intervals from the foveola to 1500-microns eccentricity and compared the mean cell counts among each group with RP. Each RP type had significantly fewer (P < .05) photoreceptors than those of the control group at each 100-microns interval. At eccentricities of 700 to 1500 microns, the retinas with X-linked and autosomal dominant RP had significantly fewer (P < .05) ganglion cells than those of the control group; the simplex RP mean ganglion cell counts were significantly lower (P < .05) than those of the control group, from 1000 to 1500 microns. The mean photoreceptor and ganglion cell counts had a .43 correlation (P < .001) in the zone of 700 to 1500 microns, consistent with transneuronal ganglion cell degeneration. Current experimental attempts to restore vision in diseased retinas by simulating or replacing photoreceptors are based on the premise that ganglion cells are retained after photoreceptor death. Our findings support this assumption.