We report the case of an otherwise healthy young adult woman who has suffered three episodes of lymphocytic meningitis of possible enteroviral aetiology during a 5 year period. Analysis of immunoglobulin subclasses has revealed a sustained reduction of IgG3 to below the fifth percentile. In addition, the patient's father and brother have a similar degree of IgG3 deficiency. Isolated IgG3 deficiency has previously been described in association with recurrent upper respiratory tract infections, asthma, obstructive lung disease and enteral infections. However, our patient did not have any of these and there was no other identifiable immune defect to account for the recurrent meningitis. Although a mere chance association is possible, the case is interesting as antibody responses involving IgG3 tend to be triggered by protein antigens such as viral envelopes, while humoral immunity is known to be important in the clearance of enteroviral infection.