We conducted a retrospective study of arsonists referred for psychiatric assessment and found that 88/202 (43.6%) had an IQ of 85 or below. The low IQ group showed more evidence of childhood temperamental disturbance, and a later pattern of internal problems rather than external factors expressing themselves as fire-setting. This study highlights the likelihood of lifelong, temperamental problems being apparent in childhood, and being predictive and possibly causative of fire setting in people with a low IQ. Better understanding of the distinct characteristics of lower IQ arsonists is essential for improved prevention, treatment and management.