Inborn Errors of Immunity (IEI) are a heterogeneous group of disorders characterised not only by an infectious diathesis, but by a wide variety of other clinical manifestations. Lymphoma is one of the most common malignancies in children and may be the first clinical manifestation of IEI, thereby 'hiding' the immune defect and delaying genetic/immunological diagnosis. Lymphomas, especially non-Hodgkin's lymphomas (NHL) are frequently associated with congenital defects of the immune system, in particular diffuse large B-cell lymphoma and Burkitt's lymphoma. Preliminary analyses conducted on 6 patients diagnosed with NHL allowed the identification of genetic variants in genes associated with IEI. In clinical practice, the diagnosis and choice of therapeutic treatment in patients with immunodeficiency-associated lymphoma are decisive and, due to the complex pathophysiology of the disease, it is not always possible to identify the boundary between benign and malignant proliferation. The identification of an undiagnosed immunodeficiency in patients with lymphoma will ensure the opportunity to apply targeted therapies, such as allogeneic haematopoietic stem cell transplantation, instead of standard clinical management based mainly on chemotherapy. The study aims to identify possible congenital defects of immunity, i.e. genetic disorders affecting the immune system, as responsible for the development of haematological malignancies. Through a multidisciplinary approach involving immunological analyses, genetic analyses and a thorough examination of clinical manifestations, we aim to characterise the immunological component underlying the development of paediatric lymphomas.