Medication errors are a common and preventable cause of patient harm. Guidance for nurses indicates that all errors and near misses should be immediately reported in order to facilitate the development of a learning culture. However, medication errors and near misses have been under-researched in mental health settings. This study explored the reasons given by psychiatric nurses for not reporting a medication error made by a colleague, and the perceived barriers to near-miss reporting. We presented 50 nurses with clinical vignettes about error and near-miss reporting and interviewed them about their likely actions and about their views and perceptions. Less than half of participants would report an error made by a colleague (48%) or a near-miss involving themselves (40%). Thematic analysis revealed common themes for both not reporting an error or a near-miss were knowledge, fear, burden of work, and excusing the error. The first three themes are similar to results obtained from research in general medical settings, but the fourth appears to be novel. Many mental health nurses are not yet fully convinced of the need to report all errors and near misses, and that improvements could be made by increasing knowledge while reducing fear, burden of work, and excusing of errors.