Two pairs of twins with chronic closed-angle glaucoma identified from the Finnish Twin Cohort Study were clinically studied by the author, and 18 other pairs of twins with the disease were ascertained from the Hospital Discharge Registry of Finland. One of the clinically studied pairs was a pair of monozygotic female twins concordant for chronic closed-angle glaucoma and the other was a pair of dizygotic female twins discordant for the disease. Of the pairs of twins ascertained from the registry one was a monozygotic male pair concordant for closed-angle glaucoma. The remaining 17 pairs (12 same-sex dizygotic and 5 monozygotic pairs) were discordant for the disease. The findings support multifactorial inheritance of chronic closed-angle glaucoma.