Classical antipsychotics like haloperidol are suggested to increase oxidative stress and oxidative cell injury in the brain. Pro-oxidant effect of haloperidol may influence the course and treatment outcomes of schizophrenia. Dietary supplementation of either antioxidants or omega-3 fatty acids was found to improve symptoms of schizophrenia. Thus we decided to assess the impact of combining omega-3 fatty acids, vitamins E and C supplementation on treatment outcome and side effects in schizophrenia patients treated with haloperidol. Ongoing haloperidol treatment of 17 schizophrenia patients was supplemented with 1000 mg capsule of omega-3 fatty acids (180 mg EPA+120 mg DHA) bid, vitamin E 400 IU bid and vitamin C 1000 mg/day. Patients were assessed with Brief Psychiatric Rating Scale (BPRS), Scale for the Assessment of Negative Symptoms (SANS), Simpson Angus Scale (SAS) and Barnes Akathisia Rating Scale (BARS) over a 4 month period. Gluthatione peroxidase, superoxide dismutase, malondialdehyde, vitamin E and C levels were also evaluated at baseline and at the end of study. BPRS, SANS, SAS and BARS scores obtained at follow-up visits were significantly lower compared to baseline. Superoxide dismutase level was significantly lower at the end of study. No significant differences were detected in other laboratory parameters. Our results support the beneficial effect of the supplementation on positive and negative symptoms of schizophrenia as well as the severity of side effects induced by haloperidol. The effect of supplementation on akathisia is especially noteworthy and it has not been investigated in previous studies.