OBJECTIVE Cognitive disorders are characterized by major impairments in functions such as memory, judgment, language and attention. One of the tests used to assess these disorders is called the Montreal Cognitive Assessment Test, which is one of the most recent tests known in this field. DMFT index is the most important dental index for evaluation of decayed, missing and filled teeth. Since alteration or damage to the sensory function of teeth can cause changes in chewing function and different levels of cognitive disorders. The objective of this study was to determine the relationship of DMFT index with cognitive disorders in people aged 25-55 in Rafsanjan in 2019. METHODS This cross-sectional study was performed on 350 patients chosen by simple random sampling within age range of 25-55 years, referred to Rafsanjan Dental School in 2019. Patients' demographic information was recorded and each was given a consent form and also Montreal Cognitive Assessment Test. Dental examination regarding decayed, missing and filled teeth was then carried out by a dentist and The DMFT index was recorded. Data were then analyzed by SPSS version 21; P value less than 0.05 was considered as significant level. RESULTS Data showed that the MOCA index had a negative significant relationship with DMFT (P = 0.001) and age (P = 0.001) and had a significant positive relationship with education (P = 0.001), but it had no significant relationship with gender (P = 0.853), time of last dental appointment (P = 0.231) and place of residence (P = 0.428). The effect of age (P = 0.67) and gender (P = 0.525) on the relationship of DMFT and MOCA was not significant. But the effect of education (P = 0.001), place of residence (P = 0.0003) and time of last dental appointment (P = 0.002) on it was significant. CONCLUSIONS The results of this study showed that the relationship between DMFT index and cognitive disorders was significant and the higher the score of this index, the more severe cognitive disorders.