The hyper-immunoglobulin M syndrome is a rare genetic disorder characterized by elevated serum IgM levels and low to undetectable levels of serum IgG, IgA. These patients characteristically present with recurrent pulmonary infections and recurrent diarrhoea. The paper reports a case of a 5-month-old baby who presented with pulmonary infection and diarrhoea. The diagnosis was made on the basis of clinical features, immune profile, whole blood flow cytometry and history in the family of three male baby siblings’ deaths due to recurrent infections.