Background: In the UK it is recommended that acetylcholinesterase inhibitors be restricted to patients with moderate Alzheimer’s disease, and progress monitored within specialist clinics. Objective: To describe a cohort of patients with Alzheimer’s disease from a whole city population treated with donepezil, and to analyse outcomes over 4 years. Methods: Historical cohort design: 88 patients recruited 1997–1998, assessed at baseline with 4-year follow-up, using an agreed protocol and validated measures: survival, retention in treatment, cognition, non-cognitive symptoms, weight change, carer stress. Results: 64.7% remained on treatment beyond 6 months, 57.9% beyond 1 year and 12.5% beyond 4 years. 56% remained alive at 4 years – almost twice the number predicted. Mean MMSE score amongst patients in treatment did not deteriorate over 4 years. Survival, retention in treatment, maintenance/improvement of cognition was greater with high baseline MMSE. Non-cognitive symptoms, carer stress and weight change remained low throughout. Conclusions: A minority of people with dementia from the population (88 of potential 2,000 at outset, 11 by 4 years) received treatment. Benefits for individuals were confirmed, especially for those with mild impairment. Expenditure on medication was modest in a population context. These findings question recent guidance from the National Institute for Clinical Excellence, which would restrict therapy to patients with moderate cognitive impairment.