A valid consent is a necessary precondition to the administration of electroconvulsive therapy (ECT). However, the assessment of mental competence to consent may be both complicated and controversial because neither case law nor statutes provide a clear description of the necessary mental abilities. The closest approximation in the literature is that derived from judicial commentary on the relevant case law and summarized into four standards. We designed a 15-item questionnaire to define and test the content or essential elements of each of these standards, and surveyed lawyers and health care professionals with known expertise or interest in the field to investigate the content validity of the questionnaire. Of the 15 items, 12 were rated important or essential to the assessment of competence to consent to ECT by > or = 67% of the lawyers and 11 were so rated by > or = 67% of the health professionals. Ten items were rated as important or essential by > or = 67% of both groups. Only two items were not so endorsed by > or = 67% of one of the groups. We conclude that the questionnaire has a satisfactory content validity and may be considered a general guideline for assessing competence to consent to ECT.