BACKGROUND: Interleukin 1β-converting enzyme (ICE) gene expression can induce neuronal apoptosis. However, the dynamic changes in ICE gene expression and its effects on neuronal apoptosis under cerebral ischemia/reperfusion conditions remain unclear. OBJECTIVE: To observe neuronal apoptosis and changes in ICE gene expression in the frontal cortex and hippocampus following ischemia/reperfusion injury. DESIGN, TIME AND SETTING: A randomized, controlled animal study was conducted at the Laboratory of Experimental Animal Center, the Second Hospital of Jilin University and Central Laboratory, the Second Hospital of Jilin University, China, from November 2008 to September 2009. MATERIALS: The ICE gene primer sequence (TaKaPa Co., Dalian, China), FACScan Flow cytometer (Becton Dickinson, Franklin Lakes, NJ, USA), and Perkin Elmer GeneAmp PCR system 2400 (Perkin Elmer, Waltham, MA, USA) were used in this study. METHODS: A total of 45 healthy, adult, male, Kunming mice were randomly assigned to normal control (n = 5), sham surgery (n = 5), and model (n = 35) groups. The mice in the model group were equally and randomly subdivided into seven subgroups according to various reperfusion time points (1 hour, 1, 3, 7, 14, 28, and 42 days). Animal models of ischemia/reperfusion injury were established by bilateral carotid artery ligation in the model group. The mice in the sham surgery group only received saline perfusion and surgery for carotid artery exposure. MAIN OUTCOME MEASURES: Neuronal apoptosis in the frontal cortex and hippocampus of mice was measured using flow cytometry. The time course of ICE mRNA levels in the frontal cortex and hippocampus were quantified using reverse transcription-polymerase chain reaction. RESULTS: Neuronal apoptosis in the frontal cortex and hippocampus peaked at 3 days following ischemia/reperfusion injury (P < 0.05). ICE mRNA expression increased in the frontal cortex at 1 day following ischemia/reperfusion injury (P < 0.05), decreased at 3 days, and then peaked at 14 days (P < 0.05). ICE mRNA expression increased in the hippocampus at 3 days following ischemia/reperfusion injury (P < 0.05), peaked at 7 days (P < 0.05), and then decreased gradually to normal levels at 28 days. CONCLUSION: Neuronal apoptosis peaked at 3 days following ischemia/reperfusion injury, and both apoptosis and ICE mRNA levels remained high for 2 weeks after injury. Early apoptosis may result from increased ICE mRNA expression.