Diffuse, cutaneous mastocytosis is a rare variant of cutaneous mast cell infiltration that can arise in neonates or infants as a generalized bullous eruption. The mode of transmission is suggested as autosomal dominant. We report four infants from two unrelated families with diffuse cutaneous mastocytosis whose cutaneous disease was not controlled by initial therapies. Treatment of the four infants with photochemotherapy dramatically reduced or eliminated symptoms. One course of therapy resulted in improvement, and retreatment has not been required two to six years later.