Rupture of intracranial aneurysm (ICA) is a rare but severe manifestation of autosomal dominant polycystic kidney disease (ADPKD). In order to assess its natural history, to determine the prevalence of familial aggregation and to document linkage to PKD1 locus, we conducted a retrospective study on 77 ADPKD patients from 64 families presenting with ruptured (N = 71) or unruptured (N = 6) aneurysm. Information was collected on kidney disease, intracranial aneurysm and family history. Linkage to PKD1 locus was examined by five probes to obtain informative flanking markers. Within one year prior to rupture, blood pressure was normal in 29% of the patients. At the time of rupture, mean age was 39.5 years (range 15 to 69), renal function was normal in half of the patients and 11% were on renal replacement therapy. The ruptured aneurysm was usually located on the middle cerebral artery. Additional intact aneurysms (1 to 6) were detected in 31% of the patients. Surgical or endovascular treatment was performed in 54 (76%) patients whereas 17 (24%) had medical management only. Rupture of ICA was fatal in seven (10%) patients. On long-term follow-up 27 (38%) were left with severe disablement. Five patients bled from another aneurysm 2 days to 14 years after initial rupture. Only two of six patients with unruptured aneurysm alone were treated on a prophylactic basis. No clinical marker associated with aneurysm was found. A family history of aneurysm rupture was demonstrated in 10 (18%) kindreds. Linkage to the PKD1 locus was established in two of three tested families.(ABSTRACT TRUNCATED AT 250 WORDS)