Objectives: Both temporomandibular disorder (TMD) and knee osteoarthritis (KOA) are prevalent joint diseases; however, an association between them has not been reported. Therefore, this study investigated the prevalence of the specific symptoms and signs of TMDs (SSTs) in patients with KOA. Methods: In total, 200 patients with KOA and 150 healthy individuals were recruited. The prevalence of specific SSTs in patients with mild or severe KOA was compared with the prevalence of specific SSTs in the control group and the results were analysed using a chi-square test. Logistic regression was used to adjust for potential confounders, such as gender and age. Results: The prevalence of 'impaired range of jaw movement (IRM)' was 63.6% (n = 77) in the mild KOA group and 62.4% (n = 117) in the severe KOA group; the values for both KOA groups were significantly higher than that for the non-OA control group (34.7%, n = 144; P < 0.017). In addition, 54.7% of the patients with severe KOA reported 'impaired temporomandibular joint (TMJ) function', a value significantly higher than that of the control group (39.6%, P < 0.017). No significant differences between groups were found for other SSTs. Conclusions: Patients with KOA might be more likely to experience SSTs, such as IRM and impaired TMJ function.