Introduction: Up to 60% of the elderly will develop delirium during the course of their hospitalization. Fewer than 50% of nurses can screen for delirium, although it is a medical emergency, and the evaluation of mental state is one of their responsibilities. Objective: To evaluate the effect of a training program on screening for delirium on the competence perception of nurses in a medicine unit. Methodology: Quasi- experimental, comparing two groups of nurses working in medicine units in two different hospitals. The independent variable, an active training taking the experience and knowledge of nurses into account, did include a tool based on the “Confusion Assessment Method.” The dependent variable, perception of competence, was measured before training and six months later with a pre-tested, self-administered questionnaire. Results: Response rate was higher than 90% at time 1 and 2. There was no difference in the perception of competence between groups before training. The experimental group improved statistically, while the comparison group did not. Conclusion: This study suggests a significant improvement in perceptions of competence following an active training, hopefully enhancing screening for delirium, and thus the well-being of hospitalized elderly patients.