There are few reliable self-report measures suitable for people with a learning disability in reporting psychological distress. This study examines the modification of the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM), exploring its reliability, using two different presentation styles. One style included a sequencing task then use of a visual histogram scale to facilitate rating; the other prompted participants to indicate presence or absence of symptoms before using the histogram. The study was conducted on a small sample of people with mental health problems who have a mild learning disability. The modified CORE-OM was found to have an excellent test-retest correlation with the group who completed the sequencing task, then the histogram scale, but the other group produced less favourable results. The preliminary results are encouraging, highlighting the need to conduct a larger study after further modifications of the measure.