Twenty-one X-chromosomal short tandem repeat loci, including the six clusters of linked markers DXS10148-DXS10135-DXS8378 (Xp22), DXS7132-DXS10074-DXS10079 (Xq12), DXS6801-DXS6809-DXS6789 (Xq21), DXS7424-DXS101 (Xq22), DXS10103-HPRTB-DXS10101 (Xq26), DXS8377-DXS10146-DXS10134-DXS7423-DXS10011 (Xq28), and the loci DXS6800 and GATA172D05 were typed in a northwestern Algerian population sample (n = 210; 104 men and 106 women). Allele and haplotype frequencies were calculated. No evidence of linkage disequilibrium was observed between pairs of loci within clusters of linked markers. At locus DXS10148, sequence analysis of a subset of alleles displaying unusual amplicon length (>/= 36 repeat units) and anomalous electrophoretic mobility showed that this marker has a complex molecular structure with different repeat variants within alleles of identical amplicon size.