Objective This 5-year longitudinal study evaluated patients with an onset of mental disorder (MD) following index emergency department (ED) visits, in terms of (1) patient profiles based on 12-month outpatient follow-up care received, (2) sociodemographic and clinical correlates, and (3) adverse health outcomes for the subsequent 2 years. Methods Data from administrative databases were collected for 2541 patients with an onset of MD, following discharge from Quebec ED. Latent class analysis was performed to identify patient profiles based on the adequacy of follow-up care after ED discharge. Bivariate analyses examined associations between class membership and sociodemographic and clinical correlates, high ED use (3 + visits/yearly), hospitalizations, and suicidal behaviors. Results Five classes of patients were identified. Class 1, the smallest, labeled “patient psychiatrist only,” included mainly young patients with serious MD. Classes 2 and 3, roughly 20%, were labeled “high use of patient general practitioner (GP) and psychiatrist” and “low use of patient GP and psychiatrist,” respectively. Both included patients with complex MD, but Class 2 had more women and older patients with chronic physical illnesses. The 2 largest classes were labeled “no usual patient service provider” (Class 5) and “patient GP only” (Class 4). Class 5 included more younger men with substance-related disorders, while Class 4 had the older patients living in rural areas, many with common MD and chronic physical illnesses. Class 3 patients had the poorest outcomes, followed by Classes 1 and 2, while Classes 4 and 5 had the best outcomes. Conclusions Results revealed that nearly 40% of patients experiencing an onset of MD received little or no outpatient care following ED discharge. Higher severity or complexity of MD and, to a lesser extent, no or low GP follow-up may explain these adverse outcomes. More adequate, continuous care, including collaborative care, is needed for these vulnerable, high-needs patients.