KNOWLEDGE of the natural history of atopic dermatitis, whether treated or untreated, is important. This includes an understanding of what is apt to happen in dermatitis from infancy to mature adult life. In evaluating any method of treatment, the natural course of the disease for the age period of the group studied must always be considered. With these points in mind, we recently completed a comprehensive study of the records of more than 2,500 patients from 2 weeks of age to late adult life. We have summarized our findings as follows. In dermatologic practice, in approximately 30 to 40% of the cases dermatitis in infants under 1 year of age was due to external sources of primary irritation and healed with simple soothing remedies. This percentage was higher in the practice of pediatricians and was about 50% in that of general practitioners. The principal causes of the dermatitis were contacts