A commissurotomy is a surgical incision of a commissure in the body, as one made in the heart to relieve constriction of the mitral valve or one made in the brain to treat certain psychiatric disorders.

Patients with scleroderma, a disease that thickens and hardens the skin, sometimes require oral commissurotomy to open the corners of the mouth, the commissures, to allow dental treatment. This procedure often leaves characteristic scars.

In neurosurgery, a commissurotomy may be performed to sever the corpus callosum; doing so has been used in cases of severe epilepsy to prevent the two hemispheres of the brain communicating.