We previously reported an association between the functional polymorphism in the upstream regulatory region of the serotonin transporter gene (SERTPR) and the prophylactic efficacy of lithium in a sample of 201 Italian subjects affected by Mood disorders. The aim of the present study was to replicate analyses on an independent sample. In total, 83 subjects affected by Bipolar disorder were recruited in the Mood Disorders Clinic of the Eginition Hospital of the Athens University, Medical School Department of Psychiatry. All patients were administered with lithium as prophylactic therapy and they were prospectively observed for at least 3 years. Subjects were typed for their SERTPR variant using polymerase chain reaction techniques. SERTPR variants were associated with lithium outcome among those subjects who had few manic episodes before lithium treatment and, as a trend, among subjects who received a high daily dose of lithium (> or =1200 mg/die). In both cases, subjects with the l/l variant showed a higher probability to develop an illness episode within 3 years of prophylactic treatment with lithium. The present study confirmed our previous observation of a better response of SERTPR*l/s carriers, but could not confirm a poor efficacy in subjects with the SERTPR*s/s genotype. Notwithstanding the conflicting results, SERTPR variants are a possible liability factor for lithium long-term efficacy in mood disorders. Further studies on independent and large samples are required to determine the reliability and direction of the possible association between SERTPR variants and lithium outcome.