The case records of 492 consecutive patients with atopic dermatitis seen at the Mayo Clinic between 1940 and 1942 were reviewed, and follow-up questionnaires were sent 20 years later. Forty-five per cent of the patients responded. We made the following observations: A family history of atopy was found in 66% of all patients presenting with atopic dermatitis. Prognosis concerning the severity of the disease, however, cannot be based on the family history. Approximately 13% of the patients having atopic dermatitis may be expected to have associated pneumonia during the course of their disease. Determination of eosinophil count in the blood is not a useful tool in predicting the severity or course of atopic dermatitis. Atopic cataracts occurred in 4% of the mild group and in 13% of the severe group. Atopic eczema was generally first noted at the age of 4 months. Only 40% of the patients with mild atopic dermatitis and only 29% of those with severe disease stated after 20 years that their dermatitis had cleared. In 11 % of the patients the eczema became localized to the hands. Asthma, hay fever, urticaria, migraine headaches, and rhinitis were found in 55% of patients having atopic dermatitis. The patients considered nervous tension, cold climate, and perspiration as the most significant causative factors. Factors most helpful in relieving atopic dermatitis were relaxation, temperate climate, topical and oral steroids, and avoidance of primary irritants. Only 5% of patients reported benefit from hyposensitization therapy.