There is accumulating evidence for the efficacy of lamotrigine in the treatment of bipolar disorder, including bipolar depression, both as monotherapy and in combination with sodium valproate. We present the cases of 3 female patients admitted to our hospital with the diagnosis of schizoaffective disorder who were treated with lamotrigine. While dosages up to 200 mg/day, resulting in serum concentrations of less than 5 mg/l, were only partially effective, 400 mg/day (with serum concentrations >10 mg/l) led to considerable mood stability, with complete remission from paranoid symptoms. We suggest that lamotrigine might be helpful in the treatment of schizoaffective disorder, probably with serum concentrations of more than 5 mg/l.