P>The purpose of this study was to determine the prevalence of temporomandibular disorder (TMD) signs and tooth wear levels in a group of hospitalised patients with mental retardation (MR). A total of 118 patients with MR and 104 mentally healthy individuals (control) were included in this study. The groups consisted of equal numbers of male and female patients. TMD signs were evaluated according to the Research Diagnostic Criteria to assess the limitation in maximum mouth opening, the alterations in the mouth opening pathway and temporomandibular joint sounds. In addition, tooth wear was recorded. The frequency of at least one sign of TMD observed in patients with MR (79 center dot 7%) was significantly higher than in controls (69 center dot 2%) (P = 0.03). In addition, 43.2% of the patients with MR had more than one sign of TMD compared with 28.8% of the control group (P = 0 center dot 02). Prevalence of each sign exhibited in the MR and control groups was as follows: limitation in mouth opening, 24 center dot 6% vs. 13 center dot 5% (P = 0 center dot 02); deviation, 18 center dot 6% vs. 26 center dot 9% (P = 0 center dot 001); deflection, 29 center dot 7% vs. 10 center dot 6% (P = 0 center dot 001); TMJ sounds, 46 center dot 6% vs. 41 center dot 1% (P = 0 center dot 43); bilateral joint sounds 28 center dot 8% vs. 16 center dot 3% (P = 0 center dot 05) respectively. Prevalences of TMD signs were not different between genders in both groups (P > 0 center dot 05). Severe tooth wear was evident in 43 center dot 2% of the patients with MR compared with 20 center dot 6% of the controls (P = 0 center dot 001). In conclusion, patients with MR seem to be more prone to having TMD signs compared with the control population.