Aim: To assess the incidence of vitamin B12 deficiency in patients with pancytopenia. Material and methods: This was a descriptive observational study carried out at Department of General Medicine, Jannayak Karpuri Thakur Medical College and Hospital, Madhepura, Bihar, India for 1 year. We included 100 patients of both sexes of age 12 years and above with pancytopenia. Complete physical and detailed clinical examination to detect pallor, jaundice, lymphadenopathy, sternal tenderness, hepatosplenomegaly was done for all the patients. Detailed neuropsychiatric evaluation was done. Serum samples were sent for vitamin B12 estimation and for biochemical investigations like liver function test, and coagulation profile testing by PT/INR, activated partial thromboplastin time. Results: A total of 100 patients with pancytopenia were included in the study. There were 62 males and 38 females with a mean ratio of 1.63:1 and with a mean age of 33.12 years. Majority (50%) of the patients presenting with pancytopenia were laborer’s. All the patients in the study were noticed with history of fatigability. 28% of the patients had bleeding manifestations in addition to easy fatigability. Only 5% of the patients presented with neurological symptoms and signs like posterior column, pyramidal involvement and psychiatric manifestations. Only 9% of the patients gave positive history of intake of drugs like metformin, proton pump inhibitors, H2 blockers etc. chronically. The most common clinical finding observed in all patients was pallor (100%). Conclusion: The study concluded that the most common cause of pancytopenia was megaloblastic anaemia. Detailed haematological investigations along with bone marrow aspiration in patients with cytopenia provided a clear understanding of disease process to identify the etiologies of pancytopenia.