median rhomboid glossists are the atrophic lesion of mid-dorsal surface of the tongue, with the incidence of 0-3.34%. It is usually with no symptoms and has an unknown etiology.In order to investigate the relationship between diabetes and MRG, 220 diabetic patients were clinically examined from those referred to Shariaty, Taleghani General Hospitals and the Institute of Metabolism and Endocrinology - Tehran during Oct 1998 to Jan 1999. A total of 220 patients were examined as control from those referred to Shahid Beheshti Dental School who had no history of any systemic disease, Smoking or the use of denture and matched by age and sex. In addition, two cytological smear samples were taken, one from MRG region and one from anterior, normal, part of the tongue of 15 proved MRG as well as 5 control cases. Results proved MRG in 10 diabetic patients and 2 control cases. This difference was statistically significant (P<0.025). Candida mycelia in MRG area was found to be 3.5 times more than normal anterior area of the tongue in diabetics (P<0.06).In conclusion: there seem to be a relationship between diabetes and the presence of MRG.