Background: There are few large population-based studies of the incidence and outcome of heart failure where the diagnosis of heart failure (HF) has been made by a General Practitioner (GP) in the community. Methods: From the General Practice Research Database in the UK, we selected a population of 686,884 people 45 years or older. Incident cases of HF in 1991 were classified definite HF, possible HF, or a first prescription of diuretics without a diagnosis of HF. The population was followed for 3-year mortality. Results: A total of 6478 patients had definite HF (mean age 77.2 years, 55.5% women), 14,050 had possible HF and 6076 persons were prescribed diuretics without a definite or possible diagnosis of HF. The overall incidence of definite HF was 9.3/1000 persons/year and of possible HF 20.2/1000 persons/year. Diuretics were prescribed for the first time for other reasons for 8.7 persons/1000/year. The incidence of HF was higher in men. The incidence of definite HF increased with age. Survival curves showed higher mortality rates in the first 3 months after the diagnosis of HF. One-year cumulative probability of death for patients with definite HF was 15.9 times higher in men and 14.7 times higher in women in comparison with the UK population. Conclusion: The diagnosis of HF by a GP successfully identifies patients at high risk of death, comparable to patients with HF identified by cardiologists on the basis of defined diagnostic criteria. HF is common in the general population, increases sharply with age, and has a poor prognosis.