This article describes age-related changes in the central nervous system pertinent to the biology of suicide, then reviews post-mortem biological studies of the brains of suicide & suicide attempters. As suicide attempts in the elderly are characterized by the use of violent means, biologic studies of impulsive violence are discussed. Data on the effect of degenerative diseases on the serotonin system & the possible link to increased suicidal behaviour in affected patients is also presented.