Oxidative stress may play a pivotal role in the pathogenesis of psoriasis, an inflammatory/hyperproliferative skin disease characterized by the cutaneous accumulation of neutrophils releasing reactive oxygen species, as revealed in a number of studies. This study was performed to demonstrate the presence of oxidative stress in psoriasis, as measured by protein oxidation markers. Twenty-nine psoriasis patients were selected based on disease severity assessment using body surface area as well as the psoriasis area severity index (PASI), and were grouped as mild (PASI a parts per thousand currency sign 10) and moderate-to-severe (PASI > 10). The measured parameters in psoriatic patients and fourteen healthy volunteers were as follows: erythrocyte sedimentation rate (ESR), high sensitive C-reactive protein (CRP), myeloperoxidase (MPO) activity, neopterin, total lipid hydroperoxides (LHP), pyrrolized protein (PP), protein carbonyl compounds (PCC), advanced oxidation protein products (AOPP), thiol levels, along with complete blood count. Except lower thiols, all parameters were found to be higher in total patients as well as in subgroups, compared to controls. There was no significant difference among the subgroups. In conclusion, protein oxidation in psoriatics, not only in moderate-to-severe, but also in mild patients, may be explained by the findings of inflammation, phagocytic cell oxidation, and MPO-hypochlorous acid-oxidation reactions; as reflected by increased total/differential leucocytes counts, CRP, ESR as well as MPO, neopterin, AOPP, PCC, PP, LHP, and decreased thiol levels. Demonstrating the AOPP and PP formation for the first time, oxidants from active neutrophils/monocytes may play an important role in the pathogenesis of psoriasis, leading to oxidative stress, especially by protein oxidation.