Sixty-eight consecutive patients with retinitis pigmentosa were studied to determine the frequency of the non-pigmented form of the disease. There was an overall incidence of 22%. Fifty percent of all cases had no characteristic pigmentation, if the duration of night vision difficulty was three years or less. The study lends statistical support to the concept that the non-pigmented form of retinitis pigmentosa is frequently an early stage of the disease and not an unusual or atypical variant. Patient without the pigmentary changes characteristic of the disorder also showed less functional impairment: the ERG b-wave was more apt to be recordable, although impaired; and the rod threshold, as determined by dark adaptation measurement, was less elevated. The clinician should suspect retinitis pigmentosa, even in the absence of pigmentary changes, if there is a family history of the disorder, night blindness, peripheral field loss, and an impaired or non-recordable electroretinographic response.