The aim of this prospective cohort study was to identify the risk factors involved in falls in 190 elderly residents of two geriatric centres in Granada (Andalusia, Spain). Because different types of falls may be associated with different factors, falls were classified according to the precipitating cause, either extrinsic or intrinsic. The incidence density and the ratios for crude and adjusted density were calculated. Cox proportional risk analysis was used to calculate adjusted incidence density ratios. Of the 121 falls identified, 63 (52.1%) had a extrinsic precipitating cause, 43 (35.5%) had an intrinsic precipitating cause, and no precipitating cause was determined in 15 falls. The rate of falls with an extrinsic precipitating cause was 0.39 per person per year, while falls with an intrinsic precipitating cause showed a frequency of 0.27 per person per year. For falls with an extrinsic precipitating cause, the most significant risk factors were: age, diabetes mellitus, a history of falling, and treatment with neuroleptics or oral bronchodilators. The number of illnesses acted as a protective factor. For falls with an intrinsic precipitating cause, the independent risk factors were: age, diabetes, dementia, alterations of gait and balance, previous falls, and treatment with digitalins, neuroleptics or antidepressants. These results suggest that the susceptibility to a fall with an intrinsic precipitating cause is easier to identify and has a greater potential for being controlled.