Severe combined immunodeficiency includes a group of diseases characterized by different inherited immunological defects. A 4-month-old girl diagnosed with Omenn syndrome, a subtype of severe combined immunodeficiency presenting with generalized erythroderma, was referred to our hospital for an allogeneic stem cell transplantation. Days before transplantation, she developed hyperpigmented macules that increased in number in the following months. As the erythroderma resolved after transplantation, diffuse hypopigmentation was simultaneously noted together with the expansion of hyperpigmented lesions. Cutaneous biopsy samples were taken at different moments, showing features of Omenn syndrome at first, and 2 months later changes consistent with hypopigmentation and repigmentation were observed. Although pigmentary disorders are rarely described in this context, these must be taken into account as a possible alternative diagnosis to graft-versus-host disease and toxicoderma in immunosuppressed patients.