Our study objective was to identify factors predicting length of hospital stay of older patients with exacerbated chronic obstructive pulmonary disease (COPD) through a multicenter, cross-sectional, retrospective study. We examined 3789 patients aged 74.3+/-11.1 years (mean+/-SD), 66.1% males, consecutively hospitalized in 32 wards of General Medicine and 31 of Geriatrics in acute care hospitals for exacerbated COPD in 10 bimonthly periods between 1988 and 1997. On admission, patients underwent a structured assessment of demographic data, nutritional status, cognitive and physical functions, comorbidity, and pharmacological therapy in the two weeks prior to admission. Patients were grouped according to whether their length of stay exceeded or not the 75th percentile of stay distribution in each bimonthly period. Variables univariately distinguishing groups were entered into a logistic regression analysis having long-stay as the dependent variable. Living alone (Odds Ratio 1.33, 95% Confidence Limits 1.03-1.70), use of more than 3 drugs prior to admission (OR 1.29, CL 1.09-1.51), use of drugs with respiratory depressant properties prior to admission (OR 1.24, CL 1.05-1.46), and the presence of more than 3 comorbid diseases (OR 1.88, CL 1.61-2.19) were independent correlates of long-stay. Age did not predict length of stay. In conclusion, selected health outcomes and indicators of disease severity, but not age, target COPD patients at risk of long-stay. Research is needed to verify whether these data can help program interventions aimed at shortening length of stay and, thus, at reducing annual hospitalization costs of the elderly.