Urticaria pigmentosa associated with Wilms tumor

Urticaria pigmentosa is the most common manifestation of mastocytosis, with the majority of cases undergoing spontaneous resolution, especially in children. Several reports have documented hematologic malignancies developing in patients with urticaria pigmentosa. We present a 4.5-year-old boy with urticaria pigmentosa who developed Wilms tumor. To our knowledge, coexisting urticaria pigmentosa and Wilms tumor have not previously been described.