Counselling is the recommended treatment for individuals with mild to moderate mental health problems of recent onset. In this evaluation of a primary care counselling service offering person-centred counselling, the Core Outcome Measure (CORE-OM) was administered at referral and at the beginning and end of therapy. A pre-post therapy effect size for 697 individuals over a 5 year period was 1.2. This compares with a waitlist (between referral and pre therapy) effect size of 0.24 for 382 individuals over a three year period. The results indicate that person-centred counselling is effective for clients with common mental health problems, such as anxiety and depression. Effectiveness is not limited to individuals with mild to moderate symptoms of recent onset, but extends to people with moderate to severe symptoms of longer duration.