Illness behavior is a well-known term often used by health professionals in clinical settings to describe specific traits and irregular observed behavior among patients. However, it is often employed on a non-theoretical basis or limited by the medical discourse either referring only to registered health-seeking behavior or to cognitive and mental representations concerning symptom attribution and feelings. This article is an attempt to analyze the concept of illness behavior, its history and application, especially in relation to functional disorders. The limitations and implications are discussed through a presentation of the development of the concept, and an alternative anthropological and sociosomatic understanding of illness behavior is developed. This understanding provides the concept with another direction and a broader empirical foundation such as accounting for social illness behavior as well as health-seeking behavior. Further with an anthropological approach illness behavior becomes situated and defined within social relations, socially positioned agents and a cultural context. This approach which is both an epistemological and methodological shift is shown to be useful and applicable in clinical settings to understand motives, practices and behaviors of individual patients. (PsycINFO Database Record (c) 2016 APA, all rights reserved).