RESUMEN
Anemia is the most common hematologic finding in patients with advanced infections caused by human immunodeficiency virus (HIV) or advanced acquired immunodeficiency syndrome (AIDS). Among many etiologies of HIV-associated anemia, vitamin B12 deficiency plays an important role, mostly due to malabsorption or HIV enteropathy. We experienced a case of megaloblastic anemia caused by vitamin B12 deficiency in a male patient with an AIDS who had no structural gastrointestinal problem. He showed severe anemia, leukopenia, thrombocytopenia and suspicious neurologic manifestations such as aggravation of dementia and gait disturbance. With vitamin B12 and folate treatment, the patient's general condition and hematologic features were improved successfully.