In France, just as in Canada, a person can be placed in preventive custody before being found guilty, to ensure the proper conduct of the investigation, to ensure that justice runs its course, or simply for reasons of security. However, the number of accused persons, and the amount of time they spend in custody, is growing significantly and alarmingly, especially in France. The following research examines the impact of preventive detention on fundamentals rights, such as the right to a fair trial. Despite the many legal guarantees surrounding preventive detention, it violates the rights of the accused in many ways by anticipating, before the actual trial, the question of guilt or innocence and the sentence applicable. In addition, the impacts of preventive detention do not affect all defendants in the same way, violating the right to equality before the law.