Background. People with a learning disability are increasingly being encouraged to take a more active role in decisions about their psychological and medical treatment, raising complex questions concerning their ability to consent. This study investigates the capacity of people with a learning disability to consent in the context of three treatment vignettes, and the influence of verbal and memory ability on this capacity.

Methods. Measures of verbal ability, memory ability and ability to consent to treatment (ACQ) were administered to 40 people with a learning disability. The ACQ consisted of three vignettes depicting a restraint, psychiatric or surgical intervention. These were followed by questions addressing people's ability to understand the presenting problem; the nature of the proposed intervention; the alternatives, risks and benefits; their involvement in the decision-making process; and their ability to express a clear decision with a rationale for treatment.

Results. Five people (12·5%) could be construed as able to consent to all three vignettes; 26 (65%) could be construed as able to consent to at least one. The questions that were most difficult to answer concerned a participants' rights, options and the impact of their choices. Verbal and memory ability both influenced ability to consent.

Conclusions. This study introduces a measure that may enable clinicians to make more systematic assessments of people's capacity to consent. A number of issues surrounding the complex area of consent to treatment are also raised.