IgG subclass deficiencies are common immune system disorders during childhood. The aim of this retrospective study was to review clinical findings and laboratory results of patients with IgG subclass deficiencies in order to determine the changes in serum IgG subclass levels during follow-up, the percentage and time span until normalization of the IgG subclass levels to age-corresponding normal levels, the type of infections incurred and the benefits of prophylaxis. Among the 59 pediatric patients reviewed, the most frequent defect was an IgG3 subclass deficiency (77%). Nine percent of the patients had an isolated IgG2 deficiency and 14% had an IgG2+G3 deficiency. The most common clinical presentations were recurrent upper respiratory tract infections, followed by pneumonia, acute gastroenteritis and urinary tract infections. Atopy was present in 15% of the patients. Ninety percent of the patients were given a prophylactic treatment (benzathine penicillin, oral antibiotics, oral bacterial lysate or intravenous immunoglobulin). The frequency of recurrent infections decreased from 13.4 +/- 7.4 per year to 5.7 +/- 3.9 in patients receiving a prophylactic regimen. Serum IgG subclass levels reached normal ranges in 30% of the patients in the IgG3 deficiency group and in 35.7% of the patients in the IgG2+G3 deficiency group. Patients with an isolated IgG2 deficiency did not reach age-related normal levels during the study period. Our study shows that IgG subclass levels may normalize in 30 to 40% of patients at about 6 years of age. We emphasize the need of monitoring IgG levels together with the clinical symptomatology in affected individuals and initiate preventive measures when appropriate.