We report a case of fibrodysplasia ossificans progressive in a 34-year-old male who presented with bilateral lower-extremity numbness. This rare disease results in abnormal ossification of various muscles, tendons, and ligaments. In this case, there was ossification of the posterior longitudinal ligament and resultant thoracic spinal-cord compression. Recognizing the MR features of this disease and this serious complication is very important in the management of these complex patients.