Limb and urinary tract defects have frequently been reported to occur together as components of a single acrorenal field defect or in many multiple malformation syndromes. However, the concordance of such anomalies has rarely been studied on a population basis or the relationships between specific limb and renal defects defined. This paper documents the patterns of acrorenal associations seen in over 1,500,000 infants born in Hungary in 1975-1984. In all, 1 in 1,800 infants had a limb deficiency and 9% of these (75 cases) had a urinary tract anomaly. Urinary tract anomalies were most commonly seen with radial ray defects, micromelia and amelia. The commonest recognized patterns were VACTERL association and the cloacal exstrophy and caudal regression sequences. Chromosomal and single gene defects also occurred. Numerical taxonomic techniques delineated six main clusters of patients. Important groupings included micromelia with renal agenesis, split hand/foot with hydronephrosis, and radial ray anomalies with VACTERL defects. The radial ray groups differed in the nature of the VACTERL anomalies seen and with respect to laterality, symmetry, and non-VACTERL anomalies. There was a strong association of bilateral limb defects with bilateral renal anomalies and unilateral with unilateral. Ipsilateral defects tended to occur in typical VACTERL cases, while contralateral defects tended to occur with additional non VACTERL midline anomalies. Although renal and limb anomalies are associated, in almost all cases malformations in other systems are also present. The precise nature of the malformation patterns seen appear to reflect differences in the nature and magnitude of the underlying dysmorphogenetic processes as well as the timing of their effects.