Membrane expression of major histocompatibility complex class II (MHC-II) molecules plays a crucial role in the presentation of antigens to CD4+ T lymphocytes and in triggering the immune response. Defects in the expression of these molecules are responsible for a combined immune deficiency and the occurrence of severe infections. We report the case of a 13-month-old infant from a second-degree consanguineous couple with a history of two early deaths in the siblings in an infectious setting. He presented with recurrent bacterial bronchopneumopathies since birth, for which immunological investigation revealed an HLA-DR deficiency. The patient was admitted at the age of 13 months with ascites and an intraperitoneal mass, the aetiological investigation of which was difficult. Tuberculosis was strongly suspected and confirmed by culture of the ascites fluid. The diagnosis of pseudotumour peritoneal tuberculosis was accepted and treatment was initiated. After an initial improvement, his tuberculosis had progressed. Despite treatment, the outcome was fatal at the age of 23 months. Our patient illustrates the difficulty of diagnosing and managing peritoneal tuberculosis in a primary immune deficiency.