A series of 153 adult arsonists is described with particular reference to motives for fire-raising and psychiatric diagnosis. All had been referred for pretrial psychiatric reports and were assessed by routine clinical methods, supplemented where possible by the Personality Assessment Schedule. The series comprised mainly men, and most were relatively young, although these are also the characteristics of criminals in general. Most suffered from some form of mental disorder. Half of them had a personality disorder and a tenth were mentally handicapped. In addition to the mentally handicapped, a further 13 per cent had a history of special schooling, so that arsonists with some educational or learning difficulties made up a quarter of the total. Revenge was the most common motive, although present in only a third of the total, and the sexual element in motivation was much less common than appears to have been the case in the past. The motive of re-housing, not previously identified, was more common in women than in men. Almost two-thirds of the properties set on fire were domestic dwellings, and over a third of arsonists were intoxicated when they started the fires. Suggestions are made for further research focusing on personality characteristics which may be associated with fire-setting.