Hyper-IgM syndrome is a rare combined immune deficiency linked to a mutation most frequently found in CD40.The diagnosis is usually made in the presence of recurrent infections, particularly pulmonary, digestive and others. Through to the dosage of lymphocyte subpopulations and after elimination of other differential diagnoses, the diagnosis of hyper-IgM syndrome can be confirmed. The objective of this work is to emphasize the presence of the diagnosis of hyper-IgM syndrome, the interest to search for it to avoid the repercussions on the growth especially and the survival. Results: We reported the case of 2 patients the first one a 4 years old patient diagnosed at the stage of complication by a DDB which presented infections essentially pulmonary with repetition in front of this table a dosage of immunoglobulins was required which was in favor of syndrome of hyper-IgM. And a second one the 10 years old, this patient who had as history a brother who died of the same symptomatology, repeated ear infections, digestive infections such as gastritis with HP a zona the immunoglobulin dosage objectified a hyper-IgM syndrome. Both patients were put under immunoglobulins with good evolution. Conclusion: The hyper IgM syndrome is still rare but should be suspected as any immune deficiency in front of repeated infections. We have illustrated in this work two cases that have evolved well with treatment and how certain complications can be avoided by early diagnosis.