Background: Anterior cruciate ligament (ACL) rupture is a common athletic injury. Multiple clinical studies have evaluated the sensitivity and specificity of physical examination tests that are used to diagnose ACL injury. We sought to determine if the sensitivity of these clinical tests is affected by a patient’s body habitus. We hypothesized that sensitivity of the Lachman, anterior drawer, and pivot shift tests is lower in obese patients than in patients with a normal body mass index (BMI). Methods: We compared the sensitivity of three clinical tests, the Lachman, anterior drawer, and pivot shift, in a group of obese patients with a group of nonobese patients. A total of 181 adult patients who had undergone ACL reconstruction by a single surgeon were included in the study. Results: Sensitivity of the Lachman test was 87.3% in obese patients versus 94.1% in the nonobese control group. Sensitivity of the anterior drawer test was 76.3% in obese patients compared to 88.2% in the nonobese control group. Sensitivity of the pivot shift test could not be accurately assessed because pain and swelling prevented the physician from performing this test in most patients on their initial presentation. Conclusions: The sensitivity of common clinical tests used to diagnose ACL tear, the Lachman, anterior drawer, and pivot shift, is decreased in obese patients compared with the nonobese control group. This study suggests that a clinician may need to have a lower threshold to perform advanced imaging in an obese patient with a suspected ligamentous injury of the knee even if the physical examination is not fully indicative of ligamentous injury. Level of Evidence: Level III.