Reticulohistiocytosis, a rare disorder occurring almost exclusively in adults, was seen in "pure" diffuse cutaneous form in an 8-year-old boy who had tuberous sclerosis since birth. The clinical features consisted of many papulonodular lesions, located mainly on the trunk and to a lesser extent on the head and limbs. Histologic findings were distinctive. Ultrastructural examination revealed the presence of pleomorphic cytoplasmic inclusions in almost all of the giant histiocytic cells of the infiltrate.