The chronic fatigue syndrome continues to occupy a tenuous position in the gray zone between “organic” and “functional” disorders. Recent research efforts have identified variations in spontaneous lymphocyte transformation and T-lymphocyte surface antigen expression in patients with chronic fatigue syndrome or similar illnesses. The roles of psychiatric conditions such as panic disorder, substance abuse, personality profiles, and learned helplessness have been further clarified. Cognitive behavioral therapy, a treatment developed for chronic pain patients, has yielded striking symptomatic improvement in sizable percentages of chronic fatigue syndrome patients.