Objectives. The primary objective is to report upon the assessments and procedures carried out in relation to an adult with learning difficulties whose competence as a witness in a criminal trial had been challenged.Design. The participant had been referred to the first author by the court for assessment in the course of a criminal trial.Method. The assessment instruments used were the WAIS‐R, GSS2, Vineland Adaptive Behaviour Scales (4th ed., Survey Version) and a set of structured questions devised for this particular participant. The functions being measured were intelligence, social function, suggestibility and the ability to accurately and truthfully report factual information.Case outcome. The participant's scores on the intelligence test brought her within the category of someone with learning difficulties, but she was found to have a high level of social functioning. She was highly suggestible, but she showed she could distinguish between false and truthful statements, despite negative feedback. The conclusion was that she would meet the requirements of a competent witness.Discussion. As a consequence of the procedures used in this case, it was decided that the approach of using a combination of standard psychometric testing and a series of structured questions was the most appropriate method of assessing witness competenc