OBJECTIVE: To study the clinical features of children with acute pancreatitis complicated by systemic inflammatory response syndrome (SIRS). METHODS: Clinical data of 71 children with acute pancreatitis from May 2005 to June 2007 were retrospectively studied. According to complications with or without SIRS, the patients were classified into two groups: SIRS (n=30) and non-SIRS (n=41). The SIRS group was subdivided into three groups based on the item number consistent with SIRS diagnostic criteria: S1 (2 items), S2 (3 items) and S3 (4 items). RESULTS: More patients had severe abdominal pain (n: 12 vs 3) and fever (n: 25 vs 15) in the SIRS group than in the non-SIRS group (P<0.01).The serum C-reactive protein (CRP) levels (49.61±8.09 mg/L) in the SIRS group were significantly higher than those in the non-SIRS group (7.98±2.82 mg/L) (P<0.01).The serum calcium level (1.93 mol/L) in the SIRS group was statistically lower than that in the non-SIRS group (2.81 mol/L)(P<0.01). Among the SIRS group, the S3 group showed the highest CRP level (120.40±10.04 mg/L), followed by the S2 group (75.78±9.50 mg/L) and S1 group (28.51±8.51 mg/L) (P<0.01). The highest sensitivity (50%) and negative predictive value (96.8%) for the diagnosis of severe acute pancreatitis was obtained for a CRP cut-off at 110 mg/L. The imaging changes were more severe in the SIRS group than in the non-SIRS group. CONCLUSIONS: Severe abdominal pain and fever were common clinical symptoms in children with acute pancreatitis complicated by SIRS. Serum CRP and calcium levels as well as imaging changes are important markers for the severity evaluation of acute pancreatitis. The patients with serum CRP level above 110 mg/L or with more than three items consistent with SIRS diagnostic criteria are at high risk for the development of severe acute pancreatitis.