Rationale, aims and objective: Introducing low intensive guided self-help interventions may offer an opportunity to decrease the high burden of mental disorders while maintaining the affordability of mental healthcare services. This study aimed to evaluate the pre- post-test effects of a low-intensive guided self-help intervention after implementation in GP practices Methods: The intervention aimed to improve coping mechanisms in order to improve mental health. It consisted of a self-help manual with therapeutic support delivered over a maximum of 8 treatment sessions. During a 36 month period, data on two outcome parameters: level of general functioning (OQ-45) and coping style (UCL), were collected from 1829 patients with an array of mental health symptoms who were referred by their GP. Measurements took place at treatment onset, following three sessions and then at treatment termination. Results: Complete results were available for 559 (31%) of the 1829 patients. No indications for an attrition bias were found. The completers analysis showed that the results regarding the OQ- and UCL-outcomes over time were statistically significant: symptom severity dropped decidedly, general functioning sharply improved and coping style was more effective than at baseline. The overall within effect size for decrease in psychological symptoms was d=0.85. Approximately 45% of the patients were either recovered or clinically improved. Conclusion: The treatment appeared to be effective in routine care while requiring considerably less therapist time than the commonly used high intensive treatments. A randomized controlled trial is now required to determine the effectiveness.