Common variable immunodeficiency (CVI) or hypogammaglobulinemia is a heterogeneous primary immunodeficiency disease in which B cells produce little or no antibody. Since the disease is relatively rare and the spectrum of associated illnesses is broad, patients are given care by a variety of specialists. Thus it has been difficult to determine the incidence of specific complications. In these studies we analyzed 103 consecutively referred CVI patients of age range 3-71 years (average, 29 years) who were followed for a period of 1-13 years (total of 750 patient years). The average serum IgG was 174.4 mg/dl for untreated patients and 301 mg/dl for patients treated with intramuscular immunoglobulin at the time of the first visit. The average IgA was 14.5, and the average IgM was 80.7, with no difference between or after immunoglobulin treatment. About one-half of the patients had T-cell dysfunction, but lymphocyte stimulation responses were inversely related to age, which implies worsened T-cell immunity with age. Serum IgG and IgA levels were found to be statistically associated (P = 0.008), and serum IgG was related to lymphocyte stimulation with concanavalin A (P = 0.01). By 1986, 79 patients were alive, 23 had died, and 1 could not be located. Recurrent bacterial illnesses were common to all patients, and 22% had developed chronic lung disease, 22% autoimmune disease, 15% cancer, 13% hepatitis, and 9% malabsorption. Autoimmune disease was more common in females, and cancer was more likely to develop in the fifth and sixth decades. In 11% of the group, other family members were found to be immunodeficient (hypogammaglobulinemic or IgA deficient). Nine patients died of respiratory insufficiency (with or without other complications), and seven patients died of cancer. These data provide valuable information about the immunologic abnormalities and the spectrum and frequency of illnesses associated with hypogammaglobulinemia.