Different Clinical Decision Support Systems (CDSS) are reported to have different effects on clinicians' performance and various factors have been shown to be responsible for that (e.g. system's advice correctness, case difficulty, users' expertise...). The aim of this study is to determine how “advice correctness” and “case difficulty” affect users accepting/rejecting the comments of the system and consequently making a right or wrong decision. It was shown that in difficult cases, users level of making mistakes in clinical decision making was significantly higher when the comments were wrong. But there was no statistically significant difference between easy and difficult cases in how users accepted/rejected correct advice.