A lobotomy (from Greek λοβός (lobos) 'lobe', and τομή (tomē) 'cut, slice') or leucotomy is a form of neurosurgical treatment for psychiatric disorder or neurological disorder (e.g. epilepsy) that involves severing connections in the brain's prefrontal cortex. The surgery causes most of the connections to and from the prefrontal cortex, the anterior part of the frontal lobes of the brain, to be severed.

In the past, this treatment was used for treating psychiatric disorders as a mainstream procedure in some countries. The procedure was controversial from its initial use, in part due to a lack of recognition of the severity and chronicity of severe and enduring psychiatric illnesses, so it was said to be an inappropriate treatment.

The originator of the procedure, Portuguese neurologist António Egas Moniz, shared the Nobel Prize for Physiology or Medicine of 1949 for the "discovery of the therapeutic value of leucotomy in certain psychoses", although the awarding of the prize has been subject to controversy.

The use of the procedure increased dramatically from the early 1940s and into the 1950s; by 1951, almost 20,000 lobotomies had been performed in the United States and proportionally more in the United Kingdom. More lobotomies were performed on women than on men: a 1951 study found that nearly 60% of American lobotomy patients were women, and limited data shows that 74% of lobotomies in Ontario from 1948 to 1952 were performed on female patients. From the 1950s onward, lobotomy began to be abandoned, first in the Soviet Union and Europe.