METHODS Recently, we reported that the serum procollagen type I carboxyterminal propeptide (P1CP) level of patients with systemic sclerosis was elevated and correlated with disease severity. In this study, the serum level of P1CP was measured using the enzyme-linked immunosorbent assay in 39 patients with localized scleroderma and in 30 control subjects. RESULTS The mean P1CP level in the patients was significantly higher than that in the normal control subjects. In 30% of the patients with localized scleroderma, the serum P1CP level was considered to be elevated (> 305 ng/mL; ie, 2 SDs above the mean control value). The mean serum P1CP level in the patients with generalized morphea was significantly higher than in the patients with morphea or linear scleroderma. In addition, the serum P1CP level in the patients with localized scleroderma was correlated with the number of sclerotic lesions, and it was negatively correlated with the duration of the disease. Anti-single-stranded DNA antibody and antihistone antibody were detected significantly more frequently in the patients with elevated P1CP than in the patients with normal P1CP. CONCLUSIONS These findings suggest that the serum P1CP level is a useful indicator of disease severity in patients with localized scleroderma, as it has been found to be in those with systemic sclerosis.