Purpose. Many studies have reported that professionals have a limited understanding of mental capacity issues. Implementation (in England and Wales) of the Mental Capacity Act (MCA) (2005) presents a challenge to services. The aim of this study was to evaluate the extent to which National Health Service (NHS) staff benefited from attending MCA training courses. Methods. Participants were assessed before and after MCA training using a structured interview, which included three scenarios describing mental capacity dilemmas, four vignettes addressing the role of the Independent Mental Capacity Advocate (IMCA), and 16 true–false items. Results. Interview performance improved post‐training, but this could be largely ascribed to an increased awareness of mental capacity issues, with minimal improvements in the knowledge that would be needed to undertake the assessments. Nine areas were identified where there remained significant gaps in participants’ knowledge post‐training. Participants with experience of dealing with mental capacity issues performed better than those without. Conclusions. The results suggest that methods other than formal training events may be needed to prepare health staff to implement new legislation.