Charles Darwin (1809-1882) suffered from a chronic illness that, throughout much of his adult life, impaired his functioning and severely limited his activities. The writings of this famous scientist as well as biographical materials indicate that he probably suffered from an anxiety disorder. His symptoms, when considered individually, suggest a variety of conditions, but taken together they point toward panic disorder with agoraphobia. This diagnosis brings coherence to Darwin's activities and explains his secluded lifestyle, including difficulty in speaking before groups and meeting with colleagues.