A 4-year-old boy with multiple café-au-lait spots and a family history of neurofibromatosis had generalized edema, histiocytic rash characterized by benign histiocytic infiltration, hepatomegaly, and life-threatening infection. Six months later, progessive splenomegaly led to juvenile chronic myelocytic leukemia that eventually proved fata. The case represents an important association of diseases.