Health anxiety is a ubiquitous experience that arises when bodily sensations or changes are believed to be indicative of a serious disease. Severe expressions of health anxiety are most often classified as hypochondriasis in the current DSM-IV-TR; however, various alternative classification schemas have been proposed for the DSM-V. Regardless of classification, severe health anxiety has significant negative impacts on well-being, social and occupational functioning, and health care resource utilization. In this review, we focus on classification issues pertinent to severe health anxiety, summarize recent research regarding potential mechanisms underlying the condition, and summarize the state of the art with respect to assessment and treatment. Future research directions are noted and suggested throughout.