PURPOSE: The purpose of this study was to determine the accuracy of 3-Tesla magnetic resonance imaging (MRI) in detecting ligamentum teres (LT) lesions in patients before they undergo hip arthroscopy for the treatment of femoroacetabular impingement. METHODS: From 2010 to 2011, data were prospectively collected on all patients presenting for treatment of hip pain. All patients underwent MRI followed by arthroscopic surgery. A radiologist prospectively documented MRI findings, and the surgeon recorded the findings at arthroscopy. Radiologic and surgical data included classification of the LT as not torn, hypertrophic, partially torn, or completely torn. All MR images were read by a single radiologist, and all surgery was performed by a single surgeon. Arthroscopy was considered the diagnostic gold standard. RESULTS: One hundred forty-two patients with a mean patient age of 35 years (range, 19 to 73 years) met the inclusion criteria. Only one complete LT tear was found in the study. The accuracy of MRI for the diagnosis of LT partial tears was 64%. The sensitivity and specificity of MRI for diagnosing partial tears of the LT were 9% and 91%, [corrected] respectively. The positive predictive value and negative predictive value were 31% and 67%, [corrected] respectively. The sensitivity and specificity of MRI for diagnosing hypertrophic LT were 32% and 78%, respectively. CONCLUSIONS: In this patient population, MRI demonstrated sensitivity and specificity of 34% and 50%, [corrected] respectively, in identifying any pathologic process of the LT. MRI is capable of ruling out [corrected] partial tears of the LT with high sensitivity (91%) and negative [corrected] predictive value (67%). LEVEL OF EVIDENCE: Level II, development of diagnostic criteria on basis of consecutive patients with universally applied gold standard.