ABSTRACTDeliberate firesetting research predominantly focuses on apprehended populations. In contrast, this paper focuses on the prevalence and characteristics of un-apprehended firesetters living in the UK. Social media was utilized to recruit 232 participants for an online questionnaire. Two hundred and twenty-five people answered a question relating to deliberate firesetting. Forty participants (17.78%) indicated that they had ignited a deliberate fire and were classified as un-apprehended firesetters. Firesetting was most common in childhood and adolescence. Relative to non-firesetters, un-apprehended deliberate firesetters were more likely to report; a diagnoses of a psychiatric illness, a diagnosis of a behavioural problem, having been suspended from school, a history of suicide attempts, experimenting with fire before the age of 10 years old, and having a family member who also ignited a deliberate fire. Un-apprehended firesetters also scored significantly higher compared to non-firesetters on the Fire Setting Scale and the Fire Proclivity Scale [Gannon, T. A., & Barrowcliffe, E. R. (2012). Firesetting in the general population: The development and validation of the Fire Setting and Fire Proclivity Scales. Legal and Criminological Psychology, 17(1), 105–122], the Fire Interest Rating Scale [Murphy, G. H., & Clare, I. C. H. (1996). Analysis of motivation in people with mild learning disabilities (mental handicap) who set fires. Psychology, Crime & Law, 2(3), 153–164], the Novaco Anger Scale and Provocation Inventory [Novaco, R. W. (2003). The Novaco Anger Scale and Provocation Inventory: NAS-PI. Los Angeles, CA: Western Psychological Services], the Boredom Proneness Scale – Short Form [Vodanovich, S. J., Wallace, J. C., & Kass, S. J. (2005). A confirmatory approach to the factor structure of the Boredom Proneness Scale: Evidence for a two-factor short form. Journal of Personality Assessment, 85(3), 295–303], and the Measure of Criminal Attitudes and Associates Scale [Mills, J. F., & Kroner, D. G. (1999). Measures of criminal attitudes and associates: User guide. Unpublished instrument and user guide].