BACKGROUND Diabetes mellitus over a period produces autonomic dysfunction. It is usually associated with poor prognosis. Reaction time is a simple noninvasive test for peripheral as well as central nervous system. Neurological deficit in patients with diabetes mellitus can be diagnosed by measurement of reaction time before it is clinically evident. Few studies have been done on the effect of type 2 diabetes mellitus on reaction time. Thus, this study was undertaken to determine the effect of type 2 diabetes mellitus on auditory and visual reaction time. MATERIALS AND METHODS 25 patients with type 2 diabetes mellitus and 25 healthy, age-matched control group were enrolled based on detailed questionnaire and informed consent was taken from all the subjects. The mean age of type 2 diabetic subjects was 48.8 years and that of control was 48 years. The subjects with type 2 diabetes were on oral medication and of more than 5 years duration. Subjects with history of alcoholism, smoking, history of hypertension, subjects on insulin, complicated cases of diabetes, subjects with visual and auditory disturbances, history of any recent illness, history of peripheral neuropathy, history of muscle weakness, severe anaemia, history of psychological disorders & neurovascular complications are excluded from the study. PC1000Hz reaction timer was used to measure auditory and visual reaction time. RESULTS Auditory and visual reaction times of type 2 diabetes mellitus patients were significantly higher as compared to those of nondiabetic control group. The p value for visual reaction time was 0.001 and that for auditory reaction time was 0.003. CONCLUSION Reaction time measurement can be used for early diagnosis of peripheral neuropathy in patients with type 2 diabetes mellitus before it is clinically manifested. Hence it can be considered as a simple non-invasive method for the early diagnosis of peripheral neuropathy in type 2 diabetes patients.