Despite the temporal trend toward decreasing length of hospital stay for all medical conditions in North America, the effect of different lengths of hospitalization on short-term outcomes such as readmission or mortality has not been well studied. However, there is growing concern that very short stays in hospital may result in premature discharges, which may lead to worse outcomes for patients. We conducted a population-based study of elderly patients with obstructive airway disease in Ontario, Canada to test the hypothesis that very short initial hospital stays increase the short-term risk for readmission and mortality. Using a cohort of 32,384 elderly patients 65 yr of age or older, we compared 15-d rates of readmission and mortality among patients with different lengths of stay. Although patients with hospital stays of less than 4 d were younger and had fewer comorbidities, they were 39% (95% confidence interval [CI], 20% to 61%) more likely to be readmitted and 45% (95% CI, 9% to 92%) more likely to die within 15 d postdischarge compared with those who stayed 4 to 6 d. The risk was highest among patients whose stay was less than or equal to 1 hospital day; they had a 69% (95% CI, 32% to 117%) excess risk of readmission and a 2.08 (95% CI, 1.23 to 3.45) -fold increase in mortality compared with those who stayed in hospital for 2 d. This suggests that some elderly patients with obstructive airway disease may be being prematurely discharged.