The causes of early rehospitalization (within 3 weeks) of very elderly patients, its possible avoidance and appropriate preventive measures were analysed retrospectively in patients of a geriatric hospital. Included were all those patients who had been admitted to the hospital from their home several (mean: five) times between 1987 and 1990 (48 women, 19 men; mean age 81.3 +/- 7.2 years--a total of 331 re-admissions). The most frequent diagnoses were heart failure (38.8%), acute cerebrovascular accident or its sequelae (31.3%), dementia (23.9%), fall or its sequelae (22.3%) and diabetes (20.9%). Of the 331 re-admissions 87 (26.3%) occurred during the first 3 weeks after discharge. The most important reasons of this early re-admissions were inadequate home care (41.4%), undesirable drug effects and non-compliance (25.3%), as well as rapid progression of the basic disease (14.9%). In the judgement of the hospital team more than 40% of the early re-admissions were avoidable, among those re-admitted because of inadequate home care and those in connection with drug intake even more than half. Early hospitalization is frequently avoidable, if individual geriatric assessment is undertaken and discharge carefully planned.