Major histocompatibility complex class II (MHCII) deficiency is a rare autosomal recessive immunodeficiency disorder characterized by lack of expression of MHCII molecules, causing defective CD4 lymphocyte function and an impaired immune response. Clinical manifestations include susceptibility to severe bacterial, viral, and fungal infections which can lead to failure to thrive and childhood death. The only definitive treatment to date is allogeneic stem cell transplantation. Here, we share our experience of 2 patients who presented with MHCII deficiency. We will discuss the role of diagnostic modalities and stem cell transplantation.