Several instances of familial Berger's disease have been reported and suggested the possible role of genetic factors in the etiology of the disease. In order to show that familial cases are not a rare finding, a french cooperative study was initiated. It revealed 34 families with 2 or 3 relatives with biopsy-proven Berger's disease. The male predominance (77%) as well as the severity of the evolution (12 out of 69 patients in terminal renal failure) in this series of familial cases are similar to those found in isolated cases. However, the young age at onset (47% being 16 years old or less) deserves to be noted. The number of familial cases is perhaps higher since 90 other families with one patient with Berger's disease and relatives either having urinary abnormalities or terminal renal failure were collected. Although in many of these last patients, clinicians strongly suspected Berger's disease, this diagnosis could not be proven in the absence of immunofluorescent study. This cooperative study has shown that two different glomerular diseases could be encountered in the same family. The association of Henoch-Schönlein purpura and Berger's disease was noted in 4 of these 34 families as well in 11 other and may represent a supplementary argument in favor of a relationship between the two diseases. However, the multiple occurrence of cases in a family may be due to chance or may be the consequence of common environmental factors and does not demonstrate the presence of genetic factors. The use of genetic markers in the families would be helpful to prove the role of these factors in Berger's disease.