Alcmaeon was born in Croton (now Crotone in Italy). Details of his work come from the surviving fragments of his book and through references by later authors, including Aristotle. He was probably influenced by the school of thought founded by Pythagoras in Croton and originated the notion that health was dependent on maintaining a balance between all the pairs of opposite qualities in the body, i.e. wet and dry, hot and cold, etc. Imbalance of these qualities resulted in illness. This theory was later developed by Hippocrates and his followers.

Alcmaeon performed dissections of animals and possibly of human cadavers also. He demonstrated various anatomical features of the eye and ear, including their connections with the brain, and correctly asserted that the brain was the control center of bodily functions and the seat of intelligence.