Objective Mental health promotion (MHP) is advocated as part of the National Service Framework (NSF) for Mental Health and the stepped-care approach to treatment in the National Institute for Clinical Excellence (NICE) guidelines. This study aimed to investigate understanding and implementation of MHP in primary care in a London borough. Design This was a cross-sectional study. Participants Participants were all general practitioners and therapists working in the primary care service (n = 30; response rate = 28%). Main outcome measures A questionnaire was designed to measure understanding of MHP, the level of MHP in the service currently, and the perceived barriers to implementing MHP. This was based on discussions with therapists working in primary care. Feedback was provided from a research tutor at the University of Surrey. Results The data show that most practitioners knew what MHP was (n = 27, 85%) and provided MHP information to patients/clients (n = 29, 97%). However, there was a lack of MHP events being offered. The difficulty in implementing these was partly ascribed to a lack of therapist time to carry out such activities. Conclusions Several recommendations were made for ameliorating the situation, for example, raising awareness of MHP and clarifying the roles of the different professionals.