Four affected members of a family with Stickler syndrome were found to have a single base-pair deletion resulting in a translational frameshift in exon 40 of the procollagen II (COL2A1) gene on chromosome 12. This mutation was not seen in any of five clinically unaffected family members or in any of 15 unrelated control patients. All affected members had distinctly abnormal vitreous syneresis and all had retinal perivascular pigmentation. Retinal detachments occurred in three of the four affected patients. Three of the four affected patients had peripheral cortical "wedge" cataracts, and the fourth had extensive nuclear sclerosis. Abnormalities of the soft palate were found in all four affected patients. All patients reported severe joint pains, and epiphyseal dysplasia was found radiographically in all patients.