Background: The Gateway Clinic is a specialist NHS service in South London providing acupuncture and Chinese medicine. The clinic receives a diverse range of referrals from an expanding population of local general practitioners (GPs). Objectives: This study explores the referral behaviour of GPs and other primary care users of the Gateway Clinic. Methods: A pragmatic mixed-methods approach was used, combining mapping of GPs’ usage of the Gateway as taken from the clinic’s database between the years 2000 and 2005, a questionnaire survey of the referring primary care practitioners in 2005, and data, including a thematic analysis of the interview transcripts from semi-structured interviews of a purposive sample of those GPs who refer. Results: Doctors in the community refer a wide range of health problems to the Gateway Clinic. The most common referrals were musculoskeletal conditions (38–44%), general and unspecified conditions (11–14%), blood and immune system conditions (6–12%), psychological conditions (8–13%), neurological conditions (6–9%), gynaecological conditions (5–6%) and digestive conditions (5–6%). The health problems referred by local healthcare practitioners correlate strongly with the patient profile seen in private acupuncture practice. Between 2000 and 2005 numbers of healthcare practitioners increased by 218% resulting in a 300% increase in patient referrals made to the clinic; the mean frequency of referral per practitioner increased by 71%. Analysis of the qualitative data suggests that positive clinical experience encourages GPs to increase the range of conditions they refer leading to the development of informal referral guidelines. Conclusion: The Gateway Clinic has become an increasingly popular referral resource. The influences that drive referral to the clinic are multiple and follow “tacit guidelines”. GPs select patients on the basis of their individual clinical experience, informed by positive patient feedback and often only after more conventional medical treatment options have been exhausted.