Throughout an illustrious scientific career, Charles Robert Darwin (1809–1882) suffered from a mysterious and disabling malady. The illness, which was characterized by depressed feelings and violent and uncomfortable cardiac palpitations, gastric upsets, and headaches, began shortly after Darwin returned from a five-year voyage to South America as the naturalist of the Beagle. One explanation for Darwin's symptoms is he suffered from Chagas’ disease as a result of being bitten by an insect common to South America. More psychodynamically oriented theorists speculate that Darwin s illness was an expression of repressed anger toward his father. Others have noted a familial vulnerability to the symptoms Darwin described. The author examines these theories and suggests that they all may have validity in explaining the mysterious illness of Charles Darwin.