This study aimed to explore the empirical trajectories of body mass index (BMI) 1 year following bariatric surgery (BS) and to identify the risk factors for each trajectory. The study included 115 patients with severe obesity who underwent BS. Assessment included metabolic variables, psychopathological and personality measures. Growth mixture modelling identified four separated trajectories for the percentage of total weight loss course shape (namely, T1 ‘good‐fast’, T2 ‘good’, T3 ‘low’ and T4 ‘low‐slow’). After adjusting for BS subtype and metabolic baseline state, T1 and T2 registered less eating and general psychopathology. T1 was characterized by the lowest scores in novelty seeking and self‐transcendence, whereas T4 was defined by the highest scores in novelty seeking and the lowest scores in persistence. Our findings suggest that psychological state prior to BS is predictive of BMI trajectories during the 12 months following BS. These results could be useful in developing more efficient interventions for these patients. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.