The aim of this study was to evaluate possible factors that predict response to treatment in subjects with temporomandibular joint (TMJ) disc displacement without reduction (DDwoR). A treatment algorithm with disc manipulation, a protrusive splint or, if unsuccessful, a stabilization splint used fulltime for 2 to 10 weeks was introduced to a consecutive series of 50 patients with TMJ DDwoR. The splint treatment non-responders were offered surgery. At the end of the splint period/after surgery, the patients rated their response to treatment on preset alternatives, according to which they were classified as responders or non-responders. In total, 44 patients were responders, ie, were completely free from symptoms or had minor discomfort on rare occasions. The remaining 6 patients still suffered moderate to severe pain. The non-responders were all women. The only statistically significant difference in baseline case-history information between the two groups was a longer duration of symptoms in the non-responder group; mean 6 years vs 2 years for the responders. All other case-history information parameters were non-significant. Conclusively, duration of symptoms was a factor of significance in predicting response to treatment. Keywords: predictor of treatment outcome, splints, TMD, TMJ disc displacement without reduction