Atopic dermatitis (AD) is a chronic inflammatory skin disease with a large impact on quality of life of the patients and their families. In most cases, the diagnosis of AD can easily be made based on (family) history and clinical examination. If necessary, a practical set of diagnostic criteria such as the UK diagnostic criteria can be used. During the diagnostic phase, it is important to pay attention to atopic comorbidity, such as allergic airway disease (allergic asthma and/or rhinitis), allergic eye disease (atopic (kerato) conjunctivitis) and immediate-type food allergy. This will not have direct consequences for the treatment of AD, but may be important for the overall well-being of the patient. Psychological factors, such as family circumstances, work/school performance and lifestyle factors should also be explored. Severity scoring using properly validated scoring lists may not be necessary for the diagnosis, however, is recommended for monitoring therapy. Simple scoring systems, such as TIS and IGA are easy to perform in daily practice. Several flare factors in AD, such as exposure to irritants or UV light, can be identified by history and clinical examination: in individual cases, additional diagnostic tests may sometimes be useful to confirm clinical suspicion. There is only limited evidence that allergen exposure to aeroallergens and/or food allergens influences AD severity. Therefore, routine allergen testing is not necessary for diagnosis and treatment of AD. The decision to perform allergen tests mainly depends on atopic comorbidity.