Psychiatric disorders in burn victims are well known and studied, but few articles treat the impact of pre-existing psychiatric pathologies on the evolution of burns. The aim of our study is to compare the evolution in terms of complications, length of stay and survival between patients with and without pre-existing mental disorders. This is a bi-centric case-control study (N = 92), conducted at the Plastic Surgery Department of Rabat University Hospital, and the Plastic Surgery Department of the Tangier-Morocco Regional Hospital, between January 2012 and February 2018. Characteristics of the patients were collected and two groups of patients were identified and compared (n = 67): a preexisting mental disorder group (n = 22) and a control group (n = 45). TBSA (total body surface area) burned and 2nd and 3rd degree burned TBSA were significantly greater in the group with a history of mental disorders compared to the control group (p = 0.012, p <0.001, p = 0.014). Mean length of stay before discharge was greater (p = 0.005). Finally, mortality in the group with pre-existing mental illness was 31.8% versus 6.7% in the control group (p = 0.011). Patients with pre-existing mental disorders seem to present worse burns and need more time to recover from them, resulting in higher morbidity and mortality and a higher cost of care. The systematic screening of burned patients in search of a psychiatric diagnosis and early management of these disorders could improve the prognosis and quality of life of these patients.