Aim: The aim of this study was to evaluate adherence to an intervention optimizing in-hospital monitoring practice, by introducing early warning scoring (EWS) of vital parameters. Background: Interventions comprising EWS systems reduce in-hospital mortality, but evaluation of adherence to such interventions is required to correctly interpret interventional outcome. Method: Adherence was evaluated with a mixed-methods approach. Quantitative data, obtained pre-interventionally (2009) and postinterventionally (2010 and 2011), were used to calculate and compare time intervals between scorings of vital parameters. Semi-structured interviews were used to evaluate the implementation process. Results: We found significant reductions in time intervals between measurements of vital parameters in 2011 compared to 2009. Scorings of vital parameters were repeated within 8 hours in 71-77% of patients scoring total modified EWS levels of 0, 2 or 4. The theme Motivation by clinical relevance and meaningfulness was identified as crucial to the implementation process. Conclusion: High adherence to an intervention may be strongly related to nurses' perceived clinical relevance of the intervention.