Clinical and light-microscopic findings were reviewed in 60 benign histiocytic tumors of the skin arising in patients who were 19 years of age or younger. These lesions were placed in five categories, based on the presence or absence of Touton giant cells, the relative content of vacuolated polygonal cells and spindle cells, and the extent of stromal collagen in the proliferations. The resulting distribution included 16 cases of classic juvenile xanthogranuloma (JXG), four examples of xanthomatous JXG. 11 “transitional” JXG, 11 histiocytomas, and 18 dermatofibromas. The histological appearances of the lesions were related to the elapsed time between their clinical presentation and biopsy sampling. Intervals of 3.5, 3.5, 3.6, 7, and 13.4 months were noted for each histologic group, respectively. Hence, “early” lesions (JXG variants) showed no differences in clinical duration, but significantly longer evolutions were observed for histiocytomas and dermatofibromas. Immunohistochemical studies were conducted utilizing antibodies to several “histiocytic” markers (CD68, cathepsin B, MAC387), CD45 antigen, and S-100 protein. Cathepsin B was universally expressed by all tumors, but its intensity and scope were variable. In addition, only dermatofibromas failed to show CD68 positivity. Scattered mononuclear inflammatory cells in the lesions were CD45 reactive, whereas other cell types were not so labeled. MAC387 was absent in all cases. These findings suggest that these lesions do indeed show histiocytic differentiation, and that they are probably related to peripheral blood monocytes antigenically. Differences in the histologic appearances of these cutaneous histiocytic proliferations of childhood may simply reflect dissimilar periods of clinical growth before biopsies are performed