Anemia is the most common pathology encountered in hematology. Etiologies are numerous, so it is important to adopt a rigorous approach. Complementary examinations must be specific to the clinical situation in order to determine the mechanisms on the one hand and decide the therapeutic management on the other. We report the observation of a case of sudden onset of profound pancytopenia. Investigation led to the diagnosis of major folic acid deficiency with favorable evolution. Through this case, we describe the diagnostic approach towards anemia and the mechanisms involved in the formation of folate deficiency.