Abstract: A 10-month-old boy presented with a history of a generalized cutaneous bullous eruption since 3 months of age. Emesis, flush, pruritus, and fatigue had accompanied relapsing episodes of sometimes extensive blistering. Histopathology showed dense dermal infiltrates of mast cells on hematoxylin and eosin and corroborating immunohistochemical staining. Laboratory examination revealed a markedly high level of serum tryptase. Based on these results and after consecutive staging, the patient was diagnosed with diffuse cutaneous bullous mastocytosis (BM). Mutation analysis detected a deletion mutation (del419) in C-Kit by direct exon sequencing. This rare entity must be considered in the differential diagnosis whenever a child presents with bullae and erosions. A crucial diagnostic hint is that rubbing of affected skin areas results in whealing (Darier’s sign). A comprehensive diagnostic approach, advanced therapeutic strategies, regular follow-ups, and instruction of patients and relatives on prevention and prophylaxis are highly indicated.