Abstract: A 6-week-old boy was referred with a generalized bullous rash since birth. Examination revealed bullous mastocytosis with initially no evidence of systemic involvement. Hepatosplenomegaly was noted at 6 months, and at 12 months he was found to have generalized lymphadenopathy. He developed bouts of vomiting associated with increased blistering. At 17 months he had sudden collapse following a brief bout of vomiting and was apneic and asystolic on arrival at the emergency department. The cause of death was attributed to massive hypotension secondary to mast cell degranulation. Although childhood mastocytosis has a favorable course in general, the subset of children with congenital bullous mastocytosis is at higher risk of sudden death and a more guarded prognosis should be given.