We report a mentally retarded 30-year-old woman with partial trisomy of chromosome 9 (46, XX-6, +der(6)t(6,9)pat) who has had epilepsy since age 11 months. She had been treated with various combinations of drugs. After 1 year of treatment with valproate (VPA) and ethosuximide (ESM), the patient developed arthralgias, muscle weakness, fatigue, and fever. Laboratory examination showed increased sedimentation rate, hypergammaglobulinemia, and high titers of antinuclear antibodies (ANA). The possibility of VPA-induced systemic lupus erythematosus (SLE) was considered. This diagnosis was supported by detection of antihistone antibodies and the HLA-DR4 antigen. VPA dosage was tapered and discontinued, with accompanying resolution of clinical, immunological and hematological signs of SLE 6 weeks after VPA discontinuation. This is the fourth reported case of VPA-induced SLE.