Common variable immunodeficiency (CVID) is a heterogeneous group of primary immunodeficiency disorders. In addition to recurrent infections and autoimmunity, cancers are more prevalent in these patients than the normal population. Increased radiosensitivity may be a reason for the increased malignancies. To analyze chromosomal radiosensitivity of CVID patients, lymphocytes were cultured from 20 CVID patients. After irradiation (50, 100 cGy), metaphases were evaluated for chromosomal aberrations. Results were compared in patients, healthy individuals, and ataxia telangiectasia as positive controls. Before irradiation there was no difference between groups of patients, but after radiation, the incidence of all kinds of aberrations was higher in the CVID patients and this was statistically significant at 100 cGy (P<0.05). CVID patients appear to be susceptible to in vitro irradiation. These patients should be protected from unnecessary radiographic diagnostic and therapeutic procedures. Also, radiosensitivity may help classifying CVID patients.