We describe a German family carrying a constitutional translocation (3;6) (p13;q25.1) in 3 consecutive generations. The only member of the family over 50 years of age and carrying the translocation developed multiple bilateral renal-cell carcinomas. We performed chromosome analysis of 4 out of 5 primary tumours, which were characterized by different clonal karyotypes. The constitutionally translocated 3p13-pter segment was lost with or without the receptor chromosome 6 in each tumour. Additional karyotypic changes were trisomy 5, 7 and 18, monosomy 14 and 21, and loss of the Y chromosome, all karyotype changes occurring frequently in sporadic non-papillary RCCs. This case is discussed with regard to the possible role of suppressor gene inactivation by constitutional translocation in the development of familial renal cancers.