A 13-year-old girl presented with significant weight loss, depression, anemia, and neutropenia. The preliminary diagnosis was anorexia nervosa combined with depression. Due to peripheral cytopenia, a bone marrow biopsy was performed to rule out leukemia. Lupus erythematosus (LE) cells were found in the bone marrow aspirate, which prompted autoantibody testing, although clinically it was not suspected the patient had systemic lupus erythematosus (SLE). Further testing demonstrated very high levels of antinuclear antibodies (ANA) (>12 U) and anti-double strand DNA (dsNDA) (>1000 IU/mL), which confirmed the diagnosis of SLE. The patient was treated with steroids for SLE, and symptoms improved quickly. In conclusion, although the identification of LE cells as one of the diagnostic criteria for SLE has been obsolete, careful examination of bone marrow to identify LE cells is still very important in the diagnosis of unsuspected SLE.