Histories of recurrent infections were obtained from 955 adults with past or present atopic dermatitis (AD) and from 199 controls. Patients who had previously been hospitalized in childhood because of severe AD had a significantly higher incidence of recurrent (greater than 5 episodes per year) cold sores and upper respiratory tract infections as well as a higher incidence of herpes zoster, than non-atopic controls. Patients with milder AD in childhood (never hospitalized) had lower incidence of these diseases, but as regards cold sores, the frequency of recurrent infections was still significantly higher than that of the controls. AD patients with past or present respiratory allergy had a slight but not statistically significant increased incidence of recurrent infections, as compared to AD patients without concomitant respiratory allergy. The factors predisposing to frequent infections appeared to be those related to severity of the atopic condition, i.e. ongoing AD, need for hospitalization in childhood and extent of dermatitis. The increased susceptibility to recurrent viral infections in AD patients is most probably related to dysfunctioning cell-mediated immunity.