Detection of mediolateral displacement of the temporomandibular joint (TMJ) meniscus and evaluation of the reducibility of this displacement are necessary because surgery is indicated when the displacement is irreducible. During TMJ arthrography, the routine sagittal study does not allow detection of this type of meniscal displacement. In a prospective study of 158 TMJ arthrograms in 83 patients, coronal radiographs were obtained and videofluoroscopy was performed (in addition to routine sagittal films and fluoroscopy) to detect mediolateral shift of the meniscus and to evaluate the reducibility of this displacement. Both upper and lower joint spaces were opacified. Coronal and lateral radiographs were obtained with the mouth open and closed. On coronal images, in 79 cases (50%) the meniscus was shifted medially, in 22 cases (14%) laterally, and in 57 cases (36%) it was in the normal position. In 90 (89%) of the 101 abnormal cases, anterior displacement was associated with a mediolateral shift. In 59 cases (58%), the mediolateral shift was irreducible. Coronal and lateral views and fluoroscopy were reviewed separately by two observers, whose conclusions were identical for all cases. In 32 (54%) of the 59 joints with irreducible mediolateral displacement, surgery was performed. For all of these, comparison of radiologic data with surgical findings indicated that coronal views and videofluoroscopy were diagnostic, whereas mediolateral displacements were not detectable on routine sagittal studies.