Objective: Small-medium enterprises (SMEs) are under-represented in occupational health research. Owner/managers face mental ill-health risks/exacerbating factors including financial stress and long hours. This study assessed the effectiveness of a mental health intervention specifically for SME owner/managers.

Methods: 297 owner/managers of SMEs were recruited and invited to complete a baseline survey assessing their mental health and wellbeing and were then randomly allocated to one of three intervention groups: 1) self-administered, 2) self-administered plus telephone, or 3) an active control condition. After a four-month intervention period they were followed up with a second survey.

Results: Intention to treat analyses showed a significant decrease in psychological distress for both the active control and the telephone facilitated intervention groups, with the telephone group demonstrating a greater ratio of change.

Conclusion: The provision of telephone support for self-administered interventions in this context appears warranted.