Introduction: Pancytopenia can be caused by underlying disorders such as certain autoimmune conditions, leukemia or even a few nutritional deficiencies such as vitamin B12 deficiency. Vitamin B12 deficiency most commonly presents as megaloblastic anemia but can also be associated with pancytopenia. It can present with a range of symptoms associated with anemia and gastrointestinal or neurological systems. Understanding the etiology of the deficiency is crucial for initiating proper treatments. Case Report: A 19-year-old patient presented with complaints of dyspnea and fever, myalgia and generalized tiredness. Examinations found him to suffer pancytopenia and esophageal candidiasis caused by vitamin B12 deficiency. This deficiency can be associated to inadequate intake and the diet of the patient as a vegetarian. Parenteral B12 treatment led the patient to symptomatically improve. Conclusion: Vitamin B12 deficiency is a reversible cause of bone marrow failure and can be easily treated if diagnosed early enough. Eggs and animal-derived foods constitute the usual source of this vitamin. Vitamin B12 deficiency should therefore be of high index suspicion to a clinician if the patient presents in similar conditions with a vegetarian diet. In the event of the deficiency being caused by inadequate intake or intrinsic factor deficiency, the treatment can be started quickly leading to the dramatic improvement of the patient’s condition