Four families with nine members affected with autosomal recessive macular dystrophy (Stargardt's Disease) and one family with six members affected with autosomal dominant macular dystrophy have been examined. Age of onset, rate of visual deterioration, fundus appearance, electroretinography and dark adaptometry have been compared in the various families. Some differences, particularly in the rate of visual deterioration and in the fundus appearance were noted between the recessive and dominant forms. Despite these differences in the clinical and related features, the genetic implications are of greater importance to the affected individuals. Genetic counselling which provides recurrence risks of the disorder in the affected individuals' siblings and children should be included in the assessment of patients with these forms of hereditary ocular disease.