BACKGROUND: Although controlled ventilation can shorten the induction time during vital capacity inhalation induction (VCII) with sevoflurane, it may associated with decrease in blood pressure and hyperventilation-related hyperdynamic responses such as hypertension and tachycardia. This study was designed to compare the clinical effects between controlled ventilation (CV) within acceptable ranges of PETCO2 and spontaneous breathing (SB) during VCII. METHODS: 100 patients were randomly allocated to the one of two groups. After the loss of consciousness during VCII with sevoflurane, controlled ventilation was applied in CV group within acceptable ranges of PETCO2 and spontaneous breathing was maintained in SB group. Alfentanil 4 mcg/kg was given i.v. 2 minutes prior to intubation. PETCO2, mean arterial pressure (MAP), heart rate (HR), SPO2, and BIS were measured at 1, 2 and 3 minute after the loss of consciousness (LOC). Clinical side effects were evaluated. RESULTS: MAP and HR were significantly decreased and increased in CV group compare to the baseline values at 1 minute after LOC. There were statistical differences of MAP and HR between two groups at 1 and 2 minutes after LOC. 46 of 50 (92%) showed delayed expiration with holding their breath > 20 s in SB group. No differences of other clinical side effects except hypotension between two groups. CONCLUSIONS: We conclude that spontaneous breathing provides a stable hemodynamic status and relatively acceptable ventilation profile compare to controlled ventilation during VCII.