AIMS AND OBJECTIVES: To estimate serum vitamin B12 levels in type 1 diabetes and to evaluate the influence of duration of diabetes, diabetic control, and age on B 12 levels. IMPORTANCE OF STUDY: Vitamin B12 deficiency is known to be associated with autoimmune disorders. However, currently there is very limited and controversial data regarding the prevalence of B12 deficiency in type 1 diabetes in South Indian population. If our study demonstrates the presence of low serum B12 levels in type1 diabetes in our population, a recommendation for regular screening and supplementation of vitamin B12 could be considered in these patients. MATERIALS AND METHODS: This was a cross- sectional study. Ninety type 1 diabetic patients (44 males and 46 females) were randomly selected based on inclusion/ exclusion criteria from the diabetes registry at Bangalore Diabetes Centre. Serum vitamin B12 level and parameters for diabetic controls were estimated using fully automated methods. All statistical analysis was carried out using SPSS version 16. RESULTS: The study showed that 45.5% of the diabetics had low B12 using the manufacturer's cut - off of 180 pg/mL and 54% had low B12 using the published cut - off of 148 pmol/l (200pg/mL). There was no significant difference in B12 levels between males and females (mean difference = - 14.3: P > 0.05). The study did not demonstrate any significant correlation between vitamin B12 levels and age, duration of diabetes, and diabetes control (the r values being - 0.18, - 0.11, and - 0.08 respectively and the P-value > 0.05). CONCLUSION: Results of our study shows the presence of low serum B12 levels in type 1 diabetics. These findings merits further research on a larger population to investigate into the cause of deficiency and the benefit of B12 supplementation in these patients.