Objective To evaluate temporomandibular disorder (TMD) treatment with a prefabricated, hydrostatic oral splint (HOS) based on self-reported patient’s symptoms using a standardized questionnaire. Methods Two hundred fifty-eight questionnaires from patients diagnosed with TMD and subsequently treated with HOS were collected from two independent private practices. Based on patient’s comfort the questionnaire recorded TMD symptoms and symptom regression. Descriptive and comparative statistics was carried out using SPSS. Results A total of 221 questionnaires were analyzed. Patients reported TMD symptoms such as pain (93.2%), TMJ clicking (66.1%), headache (25.8%), cervical spine disorders (23.5%), restricted mouth opening (22.6%) and tinnitus (11.8%). For most symptoms, improvement was reported mostly after two weeks, except for tinnitus, where positive effects were usually reported after four weeks. Conclusion HOS seem to be effective for immediate treatment of pain and other TMD symptoms. Based on the available data, a treatment period of four weeks can be recommended.