Drug induced weight gain is a serious side effect of several atypical antipsychotics. As genetic factors play an important role in the homeostasis of hunger/satiety we tried to replicate a preliminary previous finding about an impact of three polymorphisms in the synaptosomal-associated protein of 25kDa (SNAP-25; sites MnlI, TaiI and DdelI in the 3(')-UTR) on clinical response and antipsychotic induced weight gain. We genotyped 162 schizophrenic patients being treated in monotherapy with atypical antipsychotics and 312 healthy control subjects for the three polymorphisms in the SNAP-25 gene using PCR. PANSS scores and weight were measured weekly for a minimum of five weeks. We found significant associations between the TaiI and MnlI polymorphisms and serum triglyceride levels at baseline and for the DdelI polymorphism and weight gain. In conclusion our study can at least partly replicate the previous findings concerning the impact of SNAP-25 gene polymorphisms on weight gain during antipsychotic treatment.