The relationship between mental illness and firesetting remains poorly understood, with limited guidance available for clinicians required to assess mentally ill firesetters. The aim of this study was to describe firesetting behaviour, psychiatric symptoms and motivations at the time of firesetting and identify firesetter sub-groups. Arson offences referred to a Mental Health Court over a 10-year period were reviewed. Data were collected from files of 59 individuals using a structured proforma. Persecutory delusions were found to be prevalent (68%) and 58% of fires were at the patient's residence. Motivations for firesetting primarily revolved around psychosis (88%), revenge/anger (34%) and suicide (20%). Only three persons were recorded as having juvenile firesetting histories. Cluster analysis identified three sub-groups labelled "angry-antisocial," "spree firesetters" and "persecuted-suicidal." The research highlights the importance of considering multiple factors during assessment in addition to the underlying function of the firesetting.