ENT clinicians often come across children with recurrent ear, sinus and pulmonary infections. These recurrent infections, albeit common in childhood, can represent an early sign of primary immunodeficiency diseases (PIDD). PIDD is an underdiagnosed group of genetic disorders involving absent or defective components of the immune system, resulting in increased susceptibility to infections. Based on expert opinions, the Jeffrey-Modell Foundation developed 10 warning signs as a tool to assist early suspicion and diagnosis of paediatric PIDD. Among these, of relevance to ENT practice are: ≥4 new ear infections within one year, ≥2 serious sinus infections within one year, failure to thrive, persistent oral thrush, need for intravenous antibiotics to clear infections and a family history of primary immunodeficiency. To establish a diagnosis of PIDD, an immunological evaluation is guided by clinical presentation and may include a complete full blood count, serum immunoglobulins, IgG antibody titres to antibodies, lymphocyte subpopulation and serum complement. Antibody disorders are the most common type of all PIDD and require immunoglobulin replacement therapy with IgG as a standard and life-saving intervention. An appropriate serum level IgG, following replacement therapy, reduces the frequency and severity of bacterial infections and improves quality of life. This review not only focused on the importance of an early diagnosis, it also detailed the considerations of both intravenous (IVIG) and subcutaneous (SCIG) routes of IgG administration. IVIG has long been used. It is given every three-to-four weeks, has high peaks and low troughs and is commonly associated with systemic effects. On the other hand, SCIG is being increasingly used. It can be self-administered from daily to once every fortnightly, has low peak-to-trough variability and fewer systemic side-effects. As there is no universal guideline on IgG dosing, individualised treatment should be titrated based on the child’s frequency of infections.