BACKGROUND: Morbidly obese patients undergoing weight loss surgery are considered at high risk for perioperative complications and often undergo extensive testing for preoperative clearance, the necessity of which remains unproven. METHODS: We analyzed prospectively collected data from 193 patients undergoing weight loss surgery between November 2000 and November 2002. Preoperative chest x-ray, pulmonary function tests (PFTs), arterial blood gas (ABG), non-invasive cardiac testing (electrocardiogram and stress echocardiogram) and bloodwork (including anemia studies and thyroid function tests) were performed routinely in all patients. RESULTS: Mean patient age was 42±10 years, 88% were female, and the average body mass index (BMI) was 50±8 kg/m2. Preoperative testing identified abnormalities on 8 chest x-rays (4%) and 29 electrocardiograms (15%). All were minor and did not require any further investigation or management prior to surgery. PFTs were abnormal in 41 patients (21%), with obstructive physiology identified in 22 (54%), restrictive physiology in 17 (41%), and combined defects in 2 (5%). Logistic regression identified pre-existing asthma as a risk for airflow obstruction (OR: 3.3, 95% CI 1.2-8.9). ABG identified mild hypoxemia in 36 patients (17%) with only 1 (3%) severe case requiring intervention. Echocardiography demonstrated 4 abnormalities (2%), with previous history of cardiac disease as the only risk factor (OR: 14.5, 95% CI 1.8-114). Iron and vitamin B12 deficiency were identified in 31 (16%) and 12 (6%) patients, respectively, of which 84% of the former and 50% of the latter did not have anemia identified on routine complete blood count (CBC). All these patients were supplemented preoperatively. Thyroid function tests were abnormal in 6 patients (3%): 4 patients had known hypothyroidism and the other 2 had normal values on retesting. CONCLUSION: History of asthma and previous cardiac disease are strongly associated with abnormal preoperative pulmonary and cardiac testing. These tests are not mandatory as a routine preoperative evaluation and can be used selectively based on medical history. Anemia studies are helpful in identifying iron and B12 deficiencies not otherwise suspected from common preoperative screening tests.