To determine risk factors for falls, previous studies have classified falls according to the contribution of factors both intrinsic and extrinsic to the host. Due partly to the lack of operational definitions and the absence of information on reliability, no consensus on classification has been reached. Consequently, in a 3-year prospective study of falls occurring in a probability sample of community-dwelling elderly (n = 1,358), a fall classification system was developed and tested for interrater reliability. The 366 falls in the first year of the study were independently classified by two reviewers on the basis of a narrative description and structured interview. The falls in the four major categories of the classification system included: falls related to extrinsic factors (55%), falls related to intrinsic factors (39%), falls from a non-bipedal stance (8%) and unclassified falls (7%). The interrater reliability for the four major categories was 89.9% with a kappa of 0.828. The system provides operational definitions for types of falls and a reliable and flexible method for classifying falls in the elderly.