Patients with epilepsy may be subject to an increased risk of premature death from the underlying cause, or from the epilepsy itself. The extent and nature of this risk has been insufficiently investigated. Standard mortality ratios (SMRs) of patients with newly diagnosed epilepsy were determined in a prospective national population-based study. 1091 patients with newly diagnosed or suspected epilepsy were ascertained who were attending one of 275 UK general practices from 1984-1987. 1091 patients were classified after 6 months as definite epilepsy (564), possible epilepsy (228), febrile seizures (220), or not epilepsy (79). Over a median follow up of 6.9 years the SMR for patients with definite or possible epilepsy was 2.5 (95% CI 2.1-2.9), and 3.0 (2.5-3.7) for definite epilepsy. The SMR was highest during the first year after diagnosis 5.1 (3.8-6.5), declined to 2.5 (1.5-3.9) at 3 years, and 1.3 (0.7-2.0) at 5 years. The commonest causes of death were pneumonia (SMR 7.2), cancer (3.5), and stroke (3.7). The SMR for patients with idiopathic epilepsy was 1.6 (1.0-2.4), remote symptomatic epilepsy 4.3 (3.3-5.5), and acute symptomatic epilepsy 2.9 (1.7-4.5). Mortality in patients with newly-diagnosed epilepsy was high, mainly due to the underlying cause. The SMR for idiopathic epilepsy was also raised, suggesting that epilepsy per se may carry a small risk of death.