Illness anxiety disorder is a primary disorder of anxiety about having or developing a serious illness. The core feature is the cycle of worry and reassurance seeking regarding health, as opposed to a focus on relief of distress caused by somatic symptoms (as in Somatic Symptom Disorder). Clinically significant health anxiety is common, with estimates ranging up to 13% in the general adult population. There are evidence-based treatments, including psychopharmacology and cognitive behavioral therapy, that can significantly alleviate symptoms. An understanding of the core psychopathology and clinical features of illness anxiety disorder is essential to fostering a working alliance with patients with health anxiety, as is the maintenance of an empathic, curious, and nonjudgmental stance toward their anxiety. Collaboration between medical providers is essential to avoid the pitfalls of excess testing and medical treatment.