Rosacea is a chronic facial skin disease of unclear origin. Epidemiological data are scarce and controversial, with reported prevalences ranging from 0·09% to 22%. To our knowledge, incidence rates have not been quantified before.; In this observational study we quantified incidence rates of diagnosed rosacea in the U.K. and described demographic characteristics and the prevalence of ocular symptoms in patients with rosacea. We compared lifestyle factors such as smoking and alcohol consumption between patients with rosacea and controls.; Using the U.K.-based General Practice Research Database, we identified patients with an incident diagnosis of rosacea between 1995 and 2009 and matched them (1:1) to rosacea-free control patients. We assessed person-time of all patients at risk and assessed incidence rates of rosacea, stratified by age, sex, year of diagnosis and region.; We identified 60,042 rosacea cases and 60,042 controls (61·5% women). The overall incidence rate for diagnosed rosacea in the U.K. was 1·65 per 1000 person-years. Rosacea was diagnosed in some 80% of cases after the age of 30 years. Ocular symptoms were recorded in 20·8% of cases at the index date. We observed a significantly reduced relative risk of developing rosacea among current smokers (odds ratio 0·64, 95% confidence interval 0·62-0·67). Alcohol consumption was associated with a marginal risk increase.; We quantified incidence rates and characteristics of patients with rosacea diagnosed in clinical practice in a large epidemiological study using primary care data from the U.K. Smoking was associated with a substantially reduced risk of developing rosacea.