Factors initiating senile delirium were examined in 129 elderly inpatients (65 years or older). Sixty-eight patients were males and 61 females, with a mean age of 76.3 years. Delirium developed in most cases on the first two days of admission in the hospital, and the admission appeared to be a key factor precipitating delirium in about 30% of the patients. Delirium resolved or improved in 80% of the patients, but usually persisted in patients with dementia. Senile delirium tended to reappear repeatedly in patients whose episode of delirium lasted for more than 2 weeks, was associated with dementia, or had a prior history of delirium.