Background: The aim of this study was to evaluate the state of knowledge of mental capacity issues among health and social services professionals working in community teams supporting people with learning disabilities. Methods A structured interview was constructed around three scenarios, based on actual cases, concerning a financial/legal issue, a health issue and a relationships issue, as well as a set of ten "true/false" statements. The interview aimed to elicit respondents' understanding in relation, primarily, to assessment of capacity and best-interests decision making. Forty interviews were conducted (two social workers and two health professionals from each of ten community teams). Most participants had attended training on the Mental Capacity Act (2005). Results: Performance of social services and health staff was similar throughout. Fourteen areas of concern were identified where there appeared to be significant gaps in knowledge. Conclusions: Participants, particularly those who had experience of dealing with mental capacity issues, had good insight into the extent of their knowledge, and most participants said that the interview had made them aware of further training needs.