Objective To evaluate the sensitivity and specificity of arthroscopy and arthrotomy for diagnosis of medial meniscal pathology and to evaluate the diagnostic value of medial meniscal probing. Study Design Ex vivo study. Animals Cadaveric canine stifle joints (n=30). Methods Stifle joints were assigned to either a cranial cruciate ligament (CrCL) deficient or intact group. Within each stifle joint, no medial meniscal tear, a peripheral detachment, or 1 of 3 variants of vertical longitudinal tears of the medial meniscus were created. Each stifle joint had arthroscopy, craniomedial (CrMed), and caudomedial (CdMed) arthrotomy. Diagnoses were made by both observation and probing. Sensitivity, specificity, and correct classification rate (CCR) for diagnosing the state of the medial meniscus using both observation and probing with all diagnostic methods were calculated. Odds ratios were calculated to determine if probing increased diagnostic accuracy. Results Arthroscopy with probing was the most sensitive and specific diagnostic method and had the highest CCR. For arthrotomy, CrMed was the most sensitive in CrCL-deficient and CdMed the most sensitive in stable, CrCL-intact stifle joints. For all methods, probing increased their diagnostic accuracy. Conclusions Arthroscopy is the most accurate diagnostic method; however, probing the medial meniscus enhances the diagnostic accuracy of all methods. Clinical Relevance Accurate diagnosis of medial meniscal pathology is ideally achieved by means of arthroscopy; however, if arthrotomy is chosen, CrMed should be selected in unstable and CdMed in stable stifle joints. Regardless, medial meniscal probing should be performed to increase diagnostic accuracy. © 2008 by The American College of Veterinary Surgeons.