The nailfold capillary patterns of 84 patients with a variety of childhood rheumatic diseases and 34 normal control subjects were observed. Distinctive morphologic abnormalities with capillary dilation and dropout of surrounding structures were noted in two groups: patients with childhood dermatomyositis and with scleroderma (P less than 0.001). Among those with scleroderma, capillary abnormalities were found in all nine patients with systemic disease and in none of 10 patients with cutaneous disease only (Fisher's exact P less than 0.001). Of 25 patients with dermatomyositis for whom muscle biopsies were available for analysis, abnormal nailfold capillary pattern was found with highest prevalence in patients with two or more specific vascular lesions noted on biopsy (Fisher's exact P = 0.041). Nailfold capillary abnormalities are present in distinct populations of childhood rheumatic diseases, reflect the underlying vasculopathy of childhood dermatomyositis, and may be of diagnostic value in distinguishing localized from systemic scleroderma.