Purpose: To determine associations between signs and symptoms of temporomandibular disorder (TMD) and harmful oral habits. Materials and Methods: Two hundred forty-four adolescents from a public school in the city of São Roque, Brazil, were evaluated. A screening questionnaire for orofacial pain and TMD recommended by the American Academy of Orofacial Pain was used to determine signs and symptoms of TMD. Patient histories and clinical exams were used to determine harmful oral habits. Results: Eighty-three participants (34%) displayed no signs or symptoms of TMD, 161 (66%) responded affirmatively to at least one item on the questionnaire and 49 (20.1%) gave at least three affirmative responses. Headache was the most frequently reported sign or symptom of TMD (40.6%; n = 99). There was no statistically significant association between gender and signs or symptoms of TMD (P = 0.281). Twenty-five percent (n = 61) of the patients had no harmful oral habits, while 16.4% (n = 40) had only one habit, the most common of which was nail biting. A total of 20.1% (n = 49) reported two harmful oral habits and 38.5% (n = 94) reported three or more such habits. There was a statistically significant association between signs and symptoms of TMD and three or more habits. Conclusion: A statistically significant association was found between signs and/or symptoms of TMD and harmful oral habits in adolescents. Keywords: adolescent health, habits, temporomandibular joint