Omenn syndrome is a form of severe combined immunodeficiency associated with erythrodermia, hepatosplenomegaly, lymphadenopathy, and alopecia. Inherited hypomorphic mutations in the recombination activating genes 1 and 2 (RAG1 and RAG2) and in ARTEMIS genes and more recently defects in IL7RA, and RMRP genes have been described to be responsible of this peculiar immunodeficiency. The authors report here a Moroccan patient of four-months-old with classical features of Omenn syndrome, carrying a deletion at the N terminal part of RAG1. Early recognition of this condition is important for genetic counseling and early treatment.