Abstract.Three families with hereditary nephritis of Alport's type have been studied with particular emphasis on the occurrence of symptoms and signs in different sexes and age groups. Part of the material was tested for impaired hearing or eye anomalies which may be the sole manifestation of Alport's syndrome. The youngest patients were 3–4 years of age, and the proportion of diseased individuals increased with age. In two of the families about half of the investigated males or females were affected whereas in the third family all but one of 16 investigated individuals were affected. In this last family the kidney disease was exceptionally severe, but no differences in the histopathology of the kidney lesions were seen between the families. In all the families renal symptoms progressed more rapidly in males than in females. Affected as well as unaffected sons and daughters were born to healthy as well as to diseased mothers. In contrast, healthy fathers produced only unaffected children. Diseased fathers produced only daughters, two‐thirds of whom were affected. It is concluded that Alport's syndrome in these three families most probably is transmitted by autosomal dominant inheritance with variations in expression and penetra