Introduction This study measures the levels of various markers of oxidative stress and inflammation in blood samples from first-episode psychosis (FEP) patients, and examines the association between these peripheral biomarkers and cognitive performance at 6months after treatment. Methods Twenty-eight FEP patients and 28 healthy controls (matched by age, sex and educational level) had blood samples taken at admission for assessment of total antioxidant status, superoxide dismutase (SOD), total glutathione (GSH), catalase (CAT), glutathione peroxidase, lipid peroxidation, nitrites and the chemokine monocyte chemoattractant protein-1 (MCP-1). A battery of cognitive tests was also applied to the healthy controls and those FEP patients who were in remission at 6months after the acute episode. Results FEP patients had significantly lower levels of total antioxidant status, catalase and glutathione peroxidase, compared with the healthy controls. Regression analyses found that MCP-1 levels were negatively associated with learning and memory (verbal and working), nitrite levels were negatively associated with executive function, and glutathione levels were positively associated with executive function. Conclusion Our results suggest an association between certain peripheral markers of oxidative stress and inflammation and specific aspects of cognitive functioning in FEP patients. Further studies on the association between MCP-1 and cognition are warranted.