Ataxia-telangiectasia (AT) is a type of primary immunodeficiency characterized by an autosomal recessive mode of inheritance and usually presents with progressive cerebellar ataxia in early life. This complex disease is associated with humoral and cellular immune dysfunction and other features including characteristic oculocutaneous telangiectasia and increased predisposition to cancers, particularly lymphoma and leukemia. An 11-year-old Iranian girl presented with primary immunodeficiency and was diagnosed as having AT according to her clinical manifestations and molecular findings. She had a history of two types of non-Hodgkin's lymphoma and showed spontaneous regression of her diffuse large B-cell lymphoma without any specific treatment. Gene mutations and dysfunction in patients with AT result in different manifestations including abnormal development of the thymus, immunodeficiency, increased susceptibility to malignancies, and increased radiosensitivity. No standard treatment is available for these patients. The use of immunotherapeutic strategies in patients with primary immune deficiency disease-associated tumors is potentially important.