Background/aim: Psoriasis is an immune-mediated chronic inflammatory skin disease that is seen in 1%?3% of the population. It is characterized by symmetrical papulosquamous lesions on the scalp, knees, elbows, sacral region, and extensor surfaces of the extremities. Psoriasis affects both sexes equally. It is thought that reactive oxygen species have an important role in inflammatory skin diseases, especially in psoriasis. There are few studies investigating serum oxidant-antioxidant levels in psoriasis. In this study, we aimed to investigate serum oxidant and antioxidant levels in psoriasis and their effects on its pathogenesis. Materials and methods: Included in this study were 50 patients with psoriasis who had not been treated with any systemic medication and 45 healthy volunteers (control group). The total oxidant status (TOS), total antioxidant status (TAS), malondialdehyde (MDA), and 8-hydroxy 2?-deoxyguanosine (8H2D) were studied via venous blood sampling. The parameters were measured spectrophotometrically. The study was approved by the Local Ethics Committee of the Atatürk University Faculty of Medicine.Results: The mean ages of the patients and control group were 32.48 (±14.45) and 35.64 (±17.40) years, respectively. Of the patients, 23 were male and 27 were female. Of the healthy volunteers, 20 were male and 25 were female. The mean disease duration was 8.77 (±6.90) years. The mean Psoriasis Area and Severity Index (PASI) score was 11.41 (±9.62). The mean TOS levels of the patient and control groups were 63.12 (±33.23) and 4.50 (±9.74), respectively. This difference was statistically significant (P = 0.00). The mean TAS levels of the patient and control groups were 3.15 (±0.70) and 3.16 (±0.44), respectively, without any statistically significant difference. The mean MDA levels in the patient and control groups were 14.84 (±6.66) and 12.77 (±4.87), respectively, without any statistically significant difference. The mean 8H2D levels of the patient and control groups were 16,781.2 (±5918.95) and 15,276.13 (±6084.95), respectively. This difference was also not statistically significant. There was no correlation between PASI scores and the above-mentioned parameters.Conclusion: In the present study, the TOS levels showed a significant statistical difference between the psoriasis and control groups. This finding supports the effect of the oxidant system in the pathogenesis of psoriasis. This was the first study to investigate MDA, TOS, TAS, and 8H2D levels together in patients with psoriasis. More studies are needed to clearly understand the relationship between psoriasis and the oxidant-antioxidant system.