A retinitis pigmentosa (RP) population (268 eyes) had predominantly myopic refractive errors. Whereas 12% of a normal population have myopic refractions, myopia was found in 75% of 268 eyes of RP patients and in 95% of 41 eyes of X-linked RP patients. The spherical errors describe a single-peaked, skewed distribution, with a mean of -1.86 dioptres that is significantly (P less than 0.001) more myopic, by -2.93 D, than that of a normal population. The X-linked genetic group has a spherical mean of -5.51 D that is significantly (P less than 0.01) more myopic than the non-X-linked RP population. This X-linked spherical error distribution may be composed of two separate subdistributions. Astigmatic refractive errors greater than 0.5 D are found in 47% of this RP population, considerably in excess of the 19% of a normal population with such astigmatic errors.