With the availability of disease-modifying, immunomodulatory therapies (DMT) for multiple sclerosis (MS) and the first long-term studies, it became obvious that problems of compliance to complex treatment regimens under chronic conditions would also apply to these approaches. In a selective overview, problems and findings of adherence research are depicted. Based on a discussion of basic concepts, issues of operationally defining and measuring adherence are outlined. Descriptive findings on adherence to DMTs and empirical predictors of nonadherence are then discussed. Referring to theoretical models of treatment motivation, selected problems (e. g., indication) and strategies of promoting adherence are described. Finally, implications of modern concepts of the patient-therapist relationship for the issue of patient adherence are considered.