This paper reports the results of the first population-based study of the aetiology of VACTERL-association (i.e., the occurrence of three or more closely defined VACTERL-type abnormalities without other major congenital abnormalities). Forty-three VACTERL-associations and 33 VACTERL-like cases (the latter representing combinations of three or more closely or broadly defined VACTERL abnormalities with other congenital abnormalities) were evaluated. The noteworthy features of the VACTERL-association are: a significant male preponderance, a fetal weight retardation in full-term pregnancies, planned conceptions occurring later than in general and a higher incidence of infertility problems. Our data support the thesis that genetic factors are probably not involved in the aetiology of the VACTERL-association. In contrast, the VACTERL-like cases have a female excess, a higher rate of advanced birth order, no disturbance in fertility and some specific familial occurrence. These findings strongly suggest that genetic factors play a role in the aetiology of this heterogeneous group of multiple congenital abnormalities.