Background & Aims: Several single-center studies suggest that early performance of colonoscopy in Acute Lower Intestinal Bleeding (ALIB) shortens hospital length of stay (LOS). We examined predictors of LOS in ALIB using a nationally representative sample. Methods: A 20% sample of the 2002 National Inpatient Sample (NIS) part of the Health Care and Utilization Project (HCUP) was used to derive national weighted estimates. The NIS is a 20% stratified sample of all US community hospitals, representing nearly 8 million hospital discharges from 995 hospitals. Patients with a primary diagnosis of ALIB were selected using an algorithm of 60 ICD-9-CM discharge codes, excluding patients with diagnoses of upper, chronic or nonspecific intestinal bleeding. All analyses were performed using SAS-callable SUDAAN to account for complex sampling. Cox proportional hazards regression with inpatient death as the censored event was used for analyses of LOS (time to discharge). Results: Nationwide in 2002, there were an estimated 526,752 discharges with the principal diagnosis of ALIB. Fifty-six percent were female and the mean age was 70 years (interquartile range, 59-81). Common bleeding diagnoses included diverticular (42%), hemorrhoids (21%), polyp (12%), angiodysplasia (6%), ischemia (5%), and IBD (3%). Colonoscopy was performed in 52% of admissions; 57% were performed during the first day of admission (early colonoscopy). The mean hospital LOS was 6 days (interquartile range 1.8-6.2). Mean LOS was 4.7 days in admissions with early colonoscopy compared to 6.4 days in patients without (p<0.01). In the adjusted analysis, early colonoscopy was associated with a shorter LOS (hazard ratio [HR], 95% CI) (1.39,1.32-1.47). Other independent correlates of a shorter LOS included private insurance (1.25, 1.16-1.34), hemorrhoidal bleeding (1.23, 1.16-1.31) and diverticular bleeding (1.11, 1.06-1.17). Surgical intervention was independently associated with a longer LOS (0.35, 0.3-0.4), as was Deyo comorbidity score [1 (0.78, 0.74-0.82), ≥ 2 (0.62, 0.58-0.66)], ischemia (0.71, 0.65-0.77), blood transfusion(s) (0.75, 0.71-0.79), age > 70 years (0.91, 0.85-0.98), and black race (0.91, 0.85-0.98). Use of endoscopic hemostasis and weekend admission were not significantly related to LOS. Conclusions: In this nationwide study, early colonoscopy was associated with shorter hospital length of stay, though this effect did not appear to be the result of therapeutic interventions.