Purpose: Atopic dermatitis (AD) is a chronic eczematous dermatitis that has a high prevalence and diverse clinical features. Although several hypotheses about its multifactorial pathogenesis have been suggested, the cause is not yet fully understood. A better understanding of the clinical features may helpful inelucidating the pathogenesis of AD. Methods: This retrospective study analyzed the questionnaires, medical charts, and laboratory examination results of 5,000 patients diagnosed with AD at a.single tertiary hospital in Korea. Results: The demographics, allergic comorbidities, family history, severity, and treatment experiences of the patients were analyzed. Most of the patients were adults, 76.3% of whom were classified as havingan extrinsic type of AD. The mean eczema area and severity index (EASI) score was found to be 13.68, and adult patients were found to have higher severity than the other age groups. The anatomical involvements were different among the age groups, with more involvements of the head and neck in adults. The patients reported seasonal changes and stress as the factors that aggravated their symptoms the most. Topical steroids and oral cyclosporine were the most used medications at our clinic, whereas 10.1% of the patients underwent allergen -specific immunotherapy. Conclusions: This analysis of 5,000 patients would lead to a better understanding of various subtypes and diverse clinical features of AD in Koreans. Distinct characteristics were observed among different age groups; thus, treatment strategies may need to be differentiated accordingly.