This article presents the case of a patient who developed significant leukopenia after lamotrigine intake (with lower limit of the norm of neutrophils; granulocytes count was about 1,500 per mm3 but did not fall to lower values). The disease worsened over a period of about 4 years. During this time, the patient did not discontinue the drug. She continued to take lamotrigine without consulting a psychiatrist because she was convinced of its beneficial effect on her mood. After discontinuation of lamotrigine, the blood picture returned to normal within two weeks. At the same time, the patient’s mental state deteriorated significantly.