Purpose: To assess changes in the self-reported performance of smoking cessation interventions according to the 5A's model (Ask; Advise; Assess; Assist; and Arrange follow-up) among clinicians; and to identify the main barriers and facilitators in smoking cessation implementation before and after an online smoking cessation training program. Design: Pre-post evaluation. Methods: We assessed self-reported smoking cessation interventions in the implementation of the 5A's model among clinicians working in Catalan hospitals (Spain). In addition, we assessed individual-, behavioral-, and organizational-level factors that act as barriers and facilitators in the implementation of the 5A's model. We used a questionnaire of 63 items reflecting each of the 5A's performance (scored from 0 = none to 10 = most possible). The questionnaire was completed both immediately before and 6 months after the training. We analyzed the data of those participants who had a clinical role and answered pre- and post-questionnaires. We used the nonparametric test for paired data (Wilcoxon) to examine changes in scores. Findings: A total of 127 clinicians completed the pre-post questionnaire; 63.0% were registered nurses, 17.3% were nursing assistants, 7.9% were physicians, and 11.8% were other professionals (p <.001). Overall, there were significant increases in the implementation of the assist component (from a score of 4.5 to 5.2; p <.003) and arrange a follow-up component (from 3.6 to 4.5; p <.001) of the intervention. Scores in the perception of the level of overall preparation, preparedness in using smoking cessation drugs, level of competence, and organizational recognition improved (p <.001) at the follow-up; however, the score in the perception that implementing smoking cessation is part of their job decreased (from 6.3 to 4.4; p <.001). Conclusions: The online training had a positive impact on the implementation of assist and arrange follow-up components. Although self-preparedness in the management of smokers increased, the motivation and involvement of key professionals decreased. Organizational factors related to the incorporation of resources (such as protocols, records, etc.) should be improved for the correct progression of smoking cessation interventions within the institutions. Clinical Relevance: Smoking cessation training programs should incorporate some motivational content to increase the engagement of health professionals in smoking cessation interventions in their clinical practice.