Many patients attending genitourinary medicine (GUM) clinics are self referred, but some patients initially present to their general practitioner (GP). The aim of this study was to describe the referral pattern of GPs in the Lothian region of Scotland to the local GUM clinic. A questionnaire was completed by all patients referred by their GP and a case note review supplied further diagnostic and demographic information. Of 1140 (23%) patients, 965 were available for study and were referred by their GP. There was a wide variability in referral rates from different practices and from different partners within a practice. The median referral rate per 100,000 practice population was 22.4/year (range 0-586). A referral letter accompanied the patient in 797/965 (83%) cases. The detection of cases of chlamydia and gonorrhoea in patients in primary care subsequently referred to the GUM clinic was low and poor diagnostic acumen for herpes simplex virus (HSV) was notable. No consistent practice for investigation or treatment prior to referral was found and there was marked failure of the investigations initiated in primary care to achieve diagnosis. Despite this, 24% of patients were already on treatment at the time of their GUM consultation. Few STDs were diagnosed in primary care and subsequently referred to the GUM clinic suggesting either failure to diagnose infections or reluctance to refer on for confirmation, treatment, test of cure and health education.