Ten temporomandibular joints (TMJs) of 5 healthy volunteers and 19 TMJs of internal derangements in 16 patients with splint therapy were examined with MR imaging. T1-weighted images were obtained only in the closed mouth position, and gradient recalled acquisition in steady state (GRASS) images were obtained in active opening and closing phases, allowing a pseudodynamic display of TMJ movement. All patients received protrusive splint treatment. the usefulness of MR imaging to assess the efficacy of splint therapy was evaluated. Corrected disk position with the splint in place was clearly demonstrated in 9 TMJs, corresponding with elimination of reciprocal clicking. Ten other TMJs of anterior disk displacement without reduction showed uncorrected disk position by the splint. This information could confirm the therapeutic efficacy, or suggest other treatment alternatives. GRASS MR imaging can provide accurate and physiologic information about disk function in initial and follow-up assessment of protrusive splint therapy © 1992 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.