Implementation of evidence-based oral care protocols, nurse education programmes and assessment tools may reduce the risk of developing ventilator-associated pneumonia by increasing critical care nurses' knowledge and skills in adhering to current oral care recommendations. To evaluate the longitudinal effects of single-dose simulation education with structured debriefing and verbal feedback on critical care nurses' knowledge and skills in adhering to current oral care recommendations. A randomized controlled trial with repeated measurements. The data for the study were collected in a single academic centre in a 22-bed adult, mixed, medical-surgical intensive care unit in Finland from February 2012 to March 2014. The effectiveness of simulation education was evaluated through the validated Ventilator Bundle Questionnaire and Observation Schedule at baseline (n = 30) and 24 months (n = 17) after simulation education. Data were analysed using a linear mixed model and intention-to-treat analyses. During the study period, the average knowledge score in the intervention group increased significantly (44·0% to 56·0% of the total score) in the final post-intervention measurement (pt = 0·51, pg = 0·002, pt*g = 0·023). However, single-dose simulation education with structured debriefing and verbal feedback had no impact on critical care nurses' skill scores. Single-dose simulation education had only a minimal effect on critical care nurses' knowledge and skills in adhering to current oral care recommendations. Despite increased awareness, there was no significant difference in oral care practices between the study groups after simulation education. The need for regularly repeated educational sessions with theoretical training and practical exercises and direct feedback is evident. Certain aspects of oral care, such as prevention of microaspiration of oropharyngeal secretions and moistening of oral mucosa and lips, require more reinforcement than others.