The participants had been admitted to the maximum security division of a large psychiatric institution in Canada and had been included in a previous study. Every individual admitted due to firesetting over an 11-year period was included. Childhood variables, adult correctional and psychiatric variables, and characteristics of the fires they set were used to assign the participants to one of four subtypes: psychotics (33 percent), underassertives (28 percent), multi-firesetters (23 percent), and criminals (16 percent). The analysis revealed that the subtypes differed on many clinical characteristics and in their likelihood of firesetting and violent and nonviolent recidivism. Findings provided indirect support for the thesis that firesetting is often due to assertion deficits. Surprisingly, the group most likely to commit further acts of firesetting and violent offenses was the criminals, who were considerably overassertive. Tables, note, and 29 references (Author abstract modified)