IntroductionSevere obesity is the chronic disease with the highest prevalence around the world. It affects the life quality of patients in terms of physical and mental health. Although there are a variety of treatments for severe obesity, dropout rates are between 40% to 80%. ObjectiveTo identify the psychological and/or psychiatric factors presented in the initial evaluation of patients with severe obesity who deserted the preparation protocol for bariatric surgery and stablish differences between them and those who didn't defected. MethodAn analytical observational open study of cases (deserters) and controls (non deserters), retrospective, transversal, with a sample of 286 files of patients candidates for bariatric surgery from General Hospital "Dr. Manuel Gea Gonzalez" in Mexico City selected by simple random sampling fulfilling desertion variable, with a BMI of 44.77 kg/m 2 ± 7.47 and 37.45 ± 9.94 years old and were selected by non-probabilistic convenience sample. ResultsSignificant differences were found: gender (men drop out more), deserters patients showed a higher prevalence in post-traumatic stress disorder, attention deficit hyperactivity disorder, binge eating, isolation, impaired cognitive function and greater family and social dysfunction than non-deserters. A multivariate analysis of these factors showed that being male, having little social support, present a binge eating disorder, have a greater number of absences to appointments during treatment, are factors contributing to attrition. Discussion and conclusionThere are psychological/psychiatric variables that could be established as risk factors for dropping out, increasing the possibility of affecting the patient's physical and emotional well-being.Key words: Obesity, bariatric surgery, drop-out, risk factors. RESUMEN IntroducciónLa obesidad severa es la enfermedad crónica con mayor prevalencia en el mundo, afectando la calidad de vida de los pacientes. Aunque existe una variedad de tratamientos para ella, las tasas de abandono de los mismos se encuentran entre el 40-80%. ObjetivoIdentificar los factores psicológicos y/o psiquiátricos que presentaron en la evaluación inicial los pacientes con obesidad severa que desertaron del protocolo de preparación para la cirugía bariátrica y establecer diferencias con los pacientes que no desertaron. MétodoSe llevó a cabo un estudio analítico observacional de casos (desertores) y controles (no desertores), retrospectivo, transversal, con una muestra de 286 expedientes de pacientes candidatos a cirugía bariátrica del Hospital General Dr. Manuel Gea González en la Ciudad de México, con IMC de 44.77 ± 7.47 kg/m 2 y una edad de 37.45 ± 9.94 años y que fueron seleccionados por muestreo no probabilístico por conveniencia. ResultadosSe encontraron diferencias significativas: género (los hombres desertan más), los pacientes desertores mostraron una mayor prevalencia en el trastorno por estrés postraumático, trastorno por déficit de atención e hiperactividad, trastorno por atracón, aislamiento, deterioro...