Mental health problems are among the leading causes of work-related illness and sickness absence. Yet, as workplace mental health has risen up political agendas, the voice of small business is notably absent. In-depth interviews with small business owner-managers will provide foundational evidence on issues and management of mental health problems within small businesses, identifying whether concepts and understandings developed on large organisations apply to resource-constrained smaller businesses. The research will be of significance to policymakers and small business owners, and will form the basis for a scaled-up national study to develop this under-researched topic.