Although MRI has been reported to be accurate in diagnosing displaced TMJ menisci, it has not been used to characterize the condition of the meniscus. A staging system of internal derangement of the tMJ using MRI signal characteristics and morphology of the meniscus is presented. A normal meniscus has the appearance of a small drumstick and is positioned superiorly on the mandibular condyle. It produces a small amount of intermediate signal on the MRI. A grade 1 displaced meniscus has normal shape and signal; a grade 2 meniscus has normal shape and absent signal; a grade 3 meniscus has abnormal shape and absent signal. There was a significant correlation between meniscus grade and chronicity of symptoms, severity of pain, and presence of degenerative joint disease in 62 joints (39 patients).