Peroxisomal disorders are subdivided into peroxisome biogenesis disorders (PBDs) and single peroxisomal enzyme deficiencies. Diagnosis is based on clinical findings and measurement of VLCFAs and phytanic acid. Oxidative stress parameters including nitric oxide, malondialdehyde and superoxide dismutase were determined in twenty patients suspected to have peroxisomal disorders and revealed excess free radical generation. In the present study we concluded that the commonest clinical findings among our patients were neurological symptoms, developmental delay, and failure to thrive. Moreover, analysis of VLCFAs and phytanic acid levels in plasma are good diagnostic method for peroxisomal disorders. In addition, we verified a significant increase of oxidative stress parameters in peroxisomal disorders patients. The study recommends supplementation with antioxidants besides other lines of treatments.