Taking the fact that Chilean medicine saw human appearance as an indicator of what happened inside the body, this article problematizes individual corporal signs as a diagnostics tool. It approaches corporal aspects in the field of civil justice, and the uses of the body in legally and medically identifying insanity. It is based on the expert reports completed in processes of interdiction by reason of dementia during the second half of the 19th century in Santiago de Chile, with the purpose of describing the corporal base that contributed to the interpretation of mental illness and individual capacity.