Pattern reversal visual evoked potentials (PR-VEPs) of 31 patients with retinitis pigmentosa (RP) and 20 normal control subjects were recorded and compared. Recordings were taken from Oz referred to Fz, by stimulating with squares subtending 60 min, presented at a visual field of 30 degrees and 98% contrast. The mean latency of the main positive component P100 of the PR-VEP of the RP patients was 116.1 msec (SD 12.71) and 114.84 after stimulation of the left and right eye respectively. These values are significantly different (p < 0.001) from the equivalent values of the normal controls (102.5 ms (SD 5.1) and 100.6 ms (SD 4.6) for the left and right eye, respectively). Fourteen patients had a P100 latency more than 3 SDs from the normal mean value. Subsequently the patients were classified into three groups (for each eye separately) according to visual acuity (VA) and comparison for PR-VEP amplitude and latency was performed. In group A patients with VA 6/6, in B with 6/9 and in G with 6/12 or more were included. Decrease of VA was significantly associated with increased latency. The amplitude was not significantly affected except for group C. All 3 groups were not significantly different in age. The P100 in group A was consistently prolonged, compared to normals. It seems that RP can introduce significant increase in the PR-VEP latency associated with decreased VA. This may have diagnostic and prognostic implications.