Now that more than six years have elapsed since the introduction of leucotomy in this country, it is becoming possible to assess more accurately its remoter effects. The increasing use that is being made of the operation bears witness to the beneficial results that have been obtained by it, but the justifiable enthusiasm occasioned by the dramatic improvements it has produced in some cases apparently resistant to all other present-day methods of treatment must be tempered by a sober consideration of all the sequelae of section of the prefrontal fibres. While it is undoubted that after it many cases are sufficiently recovered to resume a full and satisfactory social life, and an even larger number are either freed from intense misery or from hostility and aggressive impulses and enabled to take a more co-operative part in the sheltered life of a hospital community, there are a few whose behaviour following the operation is definitely less satisfactory than it was even at the height of their illness. Furthermore, even in the successful cases, certain undesirable traits have often been noted.