The study objective was to assess the ability of computerized tomography (CT) to alter clinical decision-making in the evaluation of elderly Emergency Department (ED) patients with abdominal pain. A prospective, observational cohort study of a convenience sample of ED patients, 65 years of age, with abdominal or flank pain of 1-week duration was conducted. ED attending physicians completed a structured data collection instrument recording 5 primary endpoints before and after CT. Change in frequency of each of these 5 endpoints from pre- to post-CT comprised the target outcome variables. Of 104 eligible patients, CT altered the admission decision in 26% (95%CI 18, 34%)]; need for surgery in 12% (95% CI 6%, 18%); need for antibiotics in 21% (95% CI 13%, 29%) and suspected diagnosis in 45% (95% CI 35%, 55%). The proportion of cases in which physicians reported a high degree of certainty in the suspected diagnosis increased from 36% pre-CT (95%CI 26,44%) to 77% post-CT (95% CI 69, 85%). Diagnosis and disposition were altered by CT in about one-half and one-quarter of patients, respectively, concurrent with a doubling in diagnostic certainty. CT has the ability to significantly alter clinically important decisions in elderly patients with abdominal pain.