SummaryProteolytic imbalance may play a role in the pathogenesis of abdominal aortic aneurysms (AAA). CLG4B, which encodes the 92‐kDa form of type IV collagenase, is a candidate gene for AAA. We genotyped a polymorphic dinucleotide repeat in the 5′ flanking region of CLG4B in 94 unrelated Caucasian controls and in 127 unrelated Caucasian AAA cases. Eight alleles were detected in 188 control chromosomes with an observed heterozygosity of 0·68. There was no significant difference in allele distribution between cases and controls. We genotyped the dinucleotide repeat in 10 CEPH reference pedigrees and performed pairwise linkage analysis with markers on each of the 22 human autosomes. Lod scores between 10·45 and 20·29 were observed with markers spanning chromosome region 20q11.2‐q13.1. Further support for assignment of CLG4B to chromosome 20 was provided by analysis of human‐rodent somatic cell hybrids. This work describes a highly polymorphic marker in the CLG4B gene and assigns this gene to chr