The selection and training of future police officer candidates are two fundamental processes in achieving an effective police force. From a psychological point of view, police officer training should improve candidates' mental health, so that they can perform their police work more appropriately, benefiting not only themselves but society as a whole. This article attempts to determine whether the training given to candidates selected for training prior to being selected as officers improves their mental health. There is no precedent for research in this regard, since work in Psychology has focused on verifying that subjects do not have psychological pathologies rather than examining the effect of the training they are given. This study looks at a sample of 713 persons selected for a pre-police training program designed to allow them to subsequently join the Peruvian police force. The Derogatis SCL-90 test was used as a personality measure. The test was administered before they received training and after they had completed it (only data from subjects who passed the police entrance exam were considered). The results indicate that the training process produced no changes in personality variables that imply major psychological pathologies, but such changes did occur in variables associated with lower degree psychological pathologies. We can therefore say that there was a decline in mental health among future police officers, or an increase in their psychological pathologies. We will discuss these results and identify the limitations of the study with an eye toward further research. It is recommended that training systems be created that improve the mental health of future police officers.Keywords: police training; mental health; psychological testing; vocational selection; performance prediction Resumen Los dos procesos fundamentales para conseguir un cuerpo de policía eficaz son la selección y la formación de los candidatos a futuros policías. Desde un punto de vista psicológico, la formación que reciben los policías debe servir para conseguir trabajadores que incrementen su salud mental, de forma que puedan desempeñar la labor policial de manera más adecuada, beneficiándose no sólo ellos, sino la sociedad en su conjunto. Este trabajo trata de verificar si la formación que reciben los candidatos seleccionados para formarse previamente a ser seleccionados como policías, incrementa su salud mental. No existen trabajos previos al respecto, ya que desde la Psicología los trabajos se han centrado en verificar que los sujetos no posean problemas psicopatológicos, pero no en el efecto de la formación que se les imparte. Para llevar a cabo el estudio se contó con una muestra de 713 personas, que fueron seleccionadas para ingresar en una formación pre-policial destinada a poder ingresar con posterioridad en la policía peruana. Para medir su personalidad se utilizó la prueba SCL-90 de Derogatis, aplicando la misma antes de recibir la formación y tras terminar la misma (sólo se tuvieron en cuenta los datos de los suj...