Introduction: Diabetes Mellitus is the most prevalent endocrine disease. It causes several complications, such as retinopathy and nephropathy. The aim of this study is to evaluate the effect of diabetes mellitus on sensory-neuron auditory impairment. Materials and Methods: We conducted this case - control study during the years of 2006-2008 with the collaboration of Mashhad Diabetes Center and the Audiometric Clinic at Ghaem Hospital. Considering the inclusion and exclusion criteria, 300 diabetic patients, as the case group and 300 persons as the control group entered this study. These two groups were matched by sex and age. Audiometric examinations, consisting of Pure Tone Audiometric Test, Diapason Tests and Autoscopy were administered on the participants in the present study.Results: There was a significant difference between control and case groups in sensory-neuron auditory impairment at high and low-median frequencies. Also, there was not any association between the duration of the disease and the level of sensory-neuron auditory impairment (P>0.05). In addition, the findings indicate a significant relationship between the complicated and uncomplicated groups in terms of the level of sensory-neuron auditory impairment at high frequencies. Patients with type II Diabetes Mellitus showed prominent sensory-neuron auditory impairment at high and low-median frequencies, as compared to the control group (P<0.05). There was not such association in Type I Diabetes Mellitus (P>0.05). Furthermore, there was a significant difference between two types of Diabetes Mellitus in the level of sensory-neuron auditory impairment. which was prominent in high frequencies (P<0.05). Also, this study showed that there was not any sex difference in the sensory-neuron auditory impairment (P>0.05).Conclusion: We propose the necessity of administrating regular audiometric examinations for the patients with diabetes mellitus. Early detection of sensory-neuron auditory impairment can decrease its progression due to better glycemic control.