Background: Existing research findings indicate that minimally trained/experienced paraprofessional counsellors can be as effective as professionally trained and experienced counsellors. More research into the effectiveness of paraprofessionals with specific client populations is required to determine the conditions under which they can be most effective. Aims: To evaluate the effectiveness of a group of 12 minimally trained/experienced volunteer mental health counsellors. Method: Data were collected over a one year period on 118 clients referred to a voluntary sector counselling agency. The CORE-OM was used to measure clients' levels of distress on a session-by-session basis. Clients and counsellors also completed a range of additional self-report measures. A benchmarking strategy was used to evaluate the outcomes achieved by participants in this study against three benchmark studies selected from published literature. Results: Paraprofessionals in this study were less effective than their professional counterparts. Results showed that participants in this study achieved an effect size of .70 compared to effect sizes of 1.36, 1.39 and 1.42 in the selected benchmark studies. Implications: Findings suggest that minimally trained/experienced paraprofessional counsellors working in mental health settings may benefit from longer and more targeted training programmes before engaging in practice. Conclusions: The benchmarking strategy provided a valuable and practical means of evaluating the comparative effectiveness of paraprofessional and professional counsellors. Findings should be interpreted cautiously as the selected benchmarks are not precise measurements and may not reflect the organisational factors operating within voluntary sector counselling agencies.