A pilot study was set up to ascertain incident neurological disorders occurring in 25,000 people attending two general-practice surgeries for a period of 1 year. To achieve completeness of ascertainment and diagnostic validity poses considerable logistical and theoretical difficulties, and these are discussed. The commonest disorders (incidence in parentheses) were headaches (210/100,000), back syndromes (319/100,000), acute cerebrovascular disease (128/100,000), and migraine (64/100,000), with non-specific symptoms the most common problem overall (514/100,000). The incidence of Parkinson's disease was 26/100,000 and that of epilepsy 23/100,000. The pilot study will form the basis for a more comprehensive linkage scheme between the National Hospital for Neurology and Neurosurgery in London and surrounding general practices with a total base population of 100,000.