© 2014 British Small Animal Veterinary Association. OBJECTIVES: Serum paraoxonase 1 is considered a marker of inflammation and oxidative damage. The aims of this study were to evaluate changes in serum paraoxonase 1 activity in dogs with acute pancreatitis, to correlate serum paraoxonase 1 activity and other analytes known to be altered in dogs with pancreatitis and to assess the relationship between serum paraoxonase 1 activity and disease severity in dogs with acute pancreatitis. MATERIALS AND METHODS: Retrospective analysis of dogs with acute pancreatitis and healthy dogs in which serum paraoxonase 1 activity was measured were compared. RESULTS: Median serum paraoxonase 1 activity was significantly lower in dogs with pancreatitis (n = 19) compared to healthy ones (n = 19). Serum paraoxonase 1 activity was negatively correlated with serum lipase and amylase activities, and C-reactive protein and haptoglobin concentrations and was positively correlated with total cholesterol and glucose concentration. Disease severity was negatively correlated with serum paraoxonase 1 activity and positively correlated with triglyceride and C-reactive protein concentration. CLINICAL SIGNIFICANCE: Serum paraoxonase 1 activity is lower in dogs with acute pancreatitis and together with triglyceride and C-reactive protein concentrations is a potential marker of disease severity.