In this study, a short tandem repeat (STR) polymorphism in intron 7 of the human complement factor I (CFI) gene was studied in 637 DNA samples obtained from African, German, Thai, and Japanese populations and German and Japanese families. A total of 41 alleles were observed and classified into two groups, L and H, based on size differences. Group H, which consisted of 16 alleles, was observed only in Thai and Japanese populations at frequencies of 0.162 and 0.116, respectively, and was strongly associated with c.1217A in exon 11 (CFI*Ah). The heterozygosity values ranged from 0.89 in German to 0.93 in Thai populations. This STR would be a useful supplementary marker for forensic individualization.