Disproportionate use of emergency departments (EDs) by patients with mental disorders3 suggests the need to evaluate factors associated with ED use. Based on the Andersen 4 Behavioral model, this mixed-method study identified the contributions of predisposing, 5 enabling and needs factors in ED use among 328 patients with mental disorders. We 6 hypothesised that ED use for mental health (MH) reasons would be most strongly 7 associated with need factors. The study was conducted in four EDs located in different 8 territories of Quebec (Canada). ED teams assisted with patient recruitment. Participants 9 completed a questionnaire including a qualitative component on reasons for using the ED 10 and assessments of ED and MH services. Data were organised according to the Andersen 11 model, and analysed thematically. ED users were generally single, with low 12 socioeconomic status and inadequate knowledge of MH services (predisposing factors).