The ultrasonic cardiac output monitor is a noninvasive, quantitative method for measuring and monitoring cardiovascular hemodynamic parameters in patients. The aims of this study were first to establish reference ranges for cardiovascular indices measured by the ultrasonic cardiac output monitor in Chinese children aged 12-18 yr, second to assess the interobserver reliability of the method, and third to compare these ranges with a Caucasian group from Australia. This was a population-based cross-sectional cohort study of Chinese adolescents 12-18 years old, performed in secondary schools in Hong Kong. Ultrasonic cardiac output monitor scans were performed on each subject to measure stroke volume, cardiac output, and systemic vascular resistance together with standard oscillometric measurement of blood pressure and heart rate. Ultrasonic cardiac output monitor parameters were also standardized by deriving body surface area referenced indices. Normal ranges were defined as lying within two standard deviations on either side of the mean. To assess interobserver variability, a second, blinded operator repeated 17% of scans. A total of 590 Chinese adolescents (49% boys) were scanned. Normal ranges for cardiac output, cardiac index, stroke volume, stroke volume index, stroke volume resistance, and systemic vascular resistance index are presented. Males had a significantly higher mean stroke volume, cardiac output, and systemic vascular resistance index compared with females (p < 0.05), but no significant differences were found for the indexed values.When compared with a group of 31 Australian Caucasian adolescents (71% boys), Chinese adolescents have a significantly lower cardiac output and stroke volume (p <0.05), but these differences disappeared when adjusted for body surface area (i.e., stroke volume index, cardiac index, and systemic vascular resistance index). Interobserver variability of ultrasonic cardiac output monitor-derived stroke volume showed a coefficient of variation of 10.2%, a correlation coefficient of 0.90 (95% confidence interval 0.85-0.93), while Bland-Altman analysis showed a mean bias of 1.5% (95% limits of agreement were -19.9% to 23.0%). This study presents normal values for cardiovascular indices in Chinese adolescents using the ultrasonic cardiac output monitor. When referenced to body surface area, the differences between Caucasians and Chinese were insignificant.