In 1996, The Wesley Hospital introduced a 2 day Advanced Life Support (ALS) course, targeted at all critical care registered nurses and medical officers. The purpose of this study was to explore the retention of theoretical knowledge and clinical skills of registered nurses who had successfully completed the 2 day ALS course 18 months previously and to establish effective retesting timeframes. The study utilised a repeated post-test measure design. Forty registered nurses participated in the study. Data were collected during ALS retesting using scores from a theoretical examination and from the results of four practical skill assessments (basic life support, airway management, defibrillation and code management). Using Wilcoxon test, data were analysed with and compared to the participant's original scores from the training program 18 months previously. The findings demonstrate that the participant's theoretical knowledge remained at an equivalent level over the 18 month timeframe. However, 18 months after successfully completing an ALS course, only 75 per cent (n = 30) of participants passed the practical skill assessment components, with the 25 per cent (n = 10) requiring a second attempt to pass. The implications from this study focus on the model of assessment utilised and the dichotomy between theoretical and practical skill assessment results. Additional study is required to determine the optimal timeframe for ALS retesting and educational strategies to help retain skills over time.