A large family with myotonia dystrophica has been recognized in an isolated area of Labrador. The complete family tree showed 29 of 108 members to be affected, including an infant with the congenital form of the disease. The propositus presented with epiphora and reduced frequency of blinking, with incomplete closure--features that have not previously been stressed. Ten of the younger affected persons had no lens opacities, although most had systemic muscle signs. Slit-lamp examination was therefore not a valuable method of early detection of the disease in the family. Many of the women affected by myotonia dystrophica had obstetric complications, particularly hydramnios, premature onset of labour, necessity for cesarean section, postpartum hemorrhage and neonatal death. Hydramnios was associated in each instances with perinatal death. The fetus in each case of hydramnios may have had the gene for myotonia dystrophica. Immunoglobulin A concentrations were reduced significantly in 27 affected persons in comparison with 77 unaffected family members. There were no such differences for the other immunoglobulin classes.