In some patients with disc displacement without reduction, the symptoms of pain and decreased range of motion have been observed to resolve spontaneously over time without treatment. The natural history of this condition, however, is not well-understood. Thus, to study the natural course of disc displacement without reduction, we followed 40 patients without treatment for a period of 2.5 years. The diagnosis was established by history and physical examination and confirmed with magnetic resonance (MR) imaging. After 2.5 years, 43% of the patients were asymptomatic, 33% had decreased symptoms, and 25% of the patients showed no improvement or had required treatment. MR evidence of osteoarthritis and advanced stages of internal derangement at the initial evaluation was associated with a poor prognosis. The result of this prospective cohort study indicated that approximately 40% of patients with symptomatic disc displacement without reduction will be free of symptoms within 2.5 years, one-third will improve, whereas one-quarter will continue to be symptomatic. This knowledge should be valuable for the treatment planning and evaluation of prognosis of patients with non-reducing symptomatic disc displacement.