The prevalence of primary hypogammaglobulinaemia in Sweden was found to be at least 2.0/100,000, notwithstanding the average diagnostic delay of 12 years found in the 26 patients studied in detail in this report. Height and weight were reduced significantly in patients affected before 15 years of age, particularly in those inadequately treated. Lung function was affected in 19 patients, in 18 demonstrated by the single breath nitrogen test. According to dynamic spirometry and static lung volume measurements 8 were obstructive, 2 were restrictive and 2 had a combined impairment. Furthermore patients who had had inadequate immunoglobulin prophylaxis (less than 25 mg/kg per week) showed significantly worse lung function compared to those adequately treated. We conclude that efficient immunoglobulin prophylaxis supported by antibiotics when required, seems to promote normal growth and to inhibit development of disabling lung disease.