Schmid metaphyseal chondrodysplasia (SMCD; MIM 156500) is an autosomal dominant disorder of the skeleton that is manifested in early childhood by short stature, coxa vara, and a waddling gait. Patients with SMCD have mutations in the gene that codes for the alpha-1 chain of collagen X (COL10A1); however, mutation analysis of this gene is hampered by its size. We studied a family with SMCD: the mother, a 36-year-old woman with a height of 149 cm, had mild bilateral coxa vara. Her two sons presented with short stature, bowed legs, and coxa vara in early childhood. DNA was extracted from peripheral lymphocytes from the three patients and subjected to PCR amplification by COL10A1 gene-specific primers. In addition to single-strand conformational polymorphism (SSCP) analysis of the COL10A1 gene, we used a novel method, dideoxy fingerprinting (ddF). The genetic defect in this family was found to be a previously unreported missense mutation (T-to-C transition) at nucleotide 2011. This change resulted in a Ser-to-Pro substitution at position 671 of the carboxy-terminus of the COL10A1 protein. In addition, the two boys, but not the mother, were found to carry a trinucleotide (CCC) deletion at position 2048 of the 3' untranslated region, a polymorphism of the COL10A1 gene. We conclude that ddF can be used in the analysis of the COL10A1 gene along with SSCP. The S671P substitution is novel, but located in the same region with the other reported COL10A1 mutations, confirming type X collagen as the locus for this disease.