The aim of this study was to describe incidences of falls and fall-related injuries, and to identify predisposing factors for falls in very old people in a prospective population-based follow-up study for falls. The study is part of the Umeå 85+ Study which includes half of the population aged 85, and the total population aged 90 and > or =95 (-103), in Umeå, Sweden. Of the 253 people interviewed, 220 (87%) were followed up for falls for 6 months, of whom 109 lived in ordinary and 111 in institutional housing. A comprehensive geriatric baseline assessment was made through interviews and testing during home visits. Forty percent of the participants did fall a total 304 times, corresponding to 2.17 falls per Person Year (PY). It occurred 0.83 injuries per PY, including 0.14 fractures per PY. In a Cox regression analysis, the independent explanatory risk factors for time to first fall were dependency in activities of daily living (ADL), thyroid disorders, treatment with selective serotonin reuptake inhibitors (SSRIs) and occurrence of falls in the preceding year. It could be predicted that every seventh participant and every third of the people who did fall would suffer a fracture within 1 year. ADL, thyroid disorders and treatment with SSRIs should be considered in fall prevention programmes.