An analysis of 64 patients with congenital stationary night blindness showed that all had essentially normal fundi. Electroretinography (ERG) showed a normal a wave with extremely reduced b wave (negative type) when recorded with a single bright white stimulus in the dark. We classified these patients into two groups based on the evaluation of rod ERG and/or psychophysical dark adaptation measured with an 11 degree test target at 15 degrees in the upper part of the retina. One group (35 patients) lacked rod function (complete type). Nine patients could not be classified. No pedigree showed a complete and incomplete type in one family. Differences between the two groups in refractive error, photopic function, and oscillatory potentials in the ERG suggest a different pathogenesis. Our analysis may provide a new classification of congenital stationary night blindness with a negative ERG.