OBJECTIVES: No epidemiological data are available for hyperhidrosis (excessive sweating) in the UK, although a 2.9% prevalence rate recently was reported in a census-type study in the USA. A retrospective cohort study was designed to estimate age- and sex-specific incidence and prevalence in patients presenting to UK general practitioners over 1994-2003. Longitudinal trends including seasonality were examined and patient management was analysed in terms of prescription, referral and test rates. METHODS: The UK General Practice Research Database (GPRD) includes computerised medical records for 3 million active patients (~5% of UK population) from over 350 practices. GPRD coding dictionaries were reviewed to compile a list of hyperhidrosis-related medical codes (HMC) and prescription codes (HPC). Many HMCs and HPCs are not used exclusively for hyperhidrosis, so three cohort definitions were tested to explore their specificity and sensitivity. Prevalence was estimated by assuming that the condition is chronic with no resolution. RESULTS: In 2003 the estimated incidence of hyperhidrosis was 0.21% (n=4,267) for patients with an HMC, and 0.08% (n=1,598) for patients with an HMC and an HPC. Incidence doubled over 1994 to 2003; was 1.5 times higher in females than males; and was 1.4 times higher in summer (Apr – Sept) than winter (Oct – Mar). Prevalence was estimated at 1.62% (32,406) in 2003. There were 2,831 referrals associated with HMCs over 1994-2003, of which 986 were to pathology, 541 to general medical and only 425 to dermatology. Prescriptions for anti-perspirants were written for 6,324 patients, but only 713 received more than 5 prescriptions in total over 1994-2003. CONCLUSIONS: The GPRD is a useful tool to investigate the epidemiology and treatment of hyperhidrosis in the UK. Potential misclassification of cases was explored using different cohort definitions. Referral rates by general practitioners were low and relatively few patients persisted with anti-perspirants.