Chronic granulomatous disease is a neutrophil disorder in which phagocytic cells fail to produce a respiratory burst. Five genetic types of chronic granulomatous disease have been described and in each case the clinical manifestations relate to the inability to effectively kill catalase-positive organisms. It is classically described as a pure disorder of intracellular killing, with preservation of other aspects of phagocytic function such as migration and phagocytosis and normal function of nonmyeloid cells. This article describes a heretofore unrecognized feature of chronic granulomatous disease. Fifty-three patients with chronic granulomatous disease and 42 age-matched controls were studied by flow cytometry. Total T cell numbers and CD4 and CD8 T cell numbers were compared between patients and controls. Patients with chronic granulomatous disease had diminished T cell numbers compared to controls after 3 years of age. The difference increased with age. It is not known whether diminished T cell numbers influence the susceptibility to infections in these patients, but T cell effects could represent a significant cofactor for infection.