Multiplex abdominal aortic aneurysm families (MAAAFs) (> or =1 subject plus the proband) represent 1% to 34% of abdominal aortic aneurysm (AAA), but the percentage in France is unknown. The MAAAF rate was retrospectively defined by analysis of 3 groups: 72 of 104 consecutive individuals undergoing AAA surgery during 1994, 24 of 53 women and 35 of 76 men with giant (> or =9 cm) AAA operated on during 1986 to 1994. MAAAF characteristics were determined based on 10 families issued from these 3 groups and 34 others identified nationwide. Data were obtained from a standardized questionnaire for probands and relatives, detailed pedigrees of each family, and computed tomography (CT) scans without contrast medium of the aorta and lower limb arteries for first-degree relatives > or =40-year-of age. The MAAAF rate was 4.2% for the consecutive-surgery patients (proband M/F ratio, 17:1; mean age at surgery, 68.5 +/- 8.5 years). CT detected no additional AAA among them (screened individuals M/F ratio, 0.63; mean age, 54.0 +/- 11.2 years). MAAAF rates were 8.3% and 14.3% for the women's and giant-AAA groups with CT screening, respectively. Characteristics were investigated in 104 affected subjects from 44 MAAAFs: female relatives were more often affected than probands (P < 0.025). Compared with men, affected female relatives were significantly older at diagnosis and surgery (P < 0.05 and P < 0.02, respectively), as were affected women (P < 0.02 and P < 0.01, respectively). CT scan screening identified significantly more AAA and abdominal aortic dilatations among the 44 MAAAFs than the consecutive-surgery group (5 and 4, respectively; P < 0.001). Although the MAAAF rate seems low in France, women from MAAAF were affected more often and later, suggesting that they should be screened.