The risk of malignancy is higher in patients with Primary Immunodeficiency (PID) than in age-matched controls. Lymphoproliferative disorders are responsible for at least 50% of the cases. Patients that undergo haematopoietic stem cell transplantation (HSCT) as a curative therapy for PID are expected to have a reduced risk of malignancy, but it is unknown whether HSCT itself might increase the incidence of malignancy compared to the normal population even in the absence of radiotherapy as part of conditioning. Post transplant lymphoproliferative disorders (PTLDs), usually in association with Epstein Barr virus, may occur after HSCT, usually within 2 years, most often associated with T-lymphocyte depletion and intense immunosuppression, for example in the context of graft versus host disease (GvHD). Data are sparse on occurrence of non-PTLD malignancy post-HSCT in patients with PID. Underlying genetic disease, tissue distribution of genetic defect, GvHD, viral infections and extent of donor chimerism may be important factors that play a role in PID patients developing malignancies post-HSCT.