- Aim: To analyze trends in childhood body mass index (BMI) in Israel between 1990 and 2000, and to determine the proportion of obese children using US and population-specific reference values. Methods: Cross-sectional data from 13 284 second- and fifth-grade schoolchildren were collected, including age, sex, height, weight, country of birth, and time since immigration. Age- and sex-specific BMI means and centiles were calculated, and the prevalence of obesity was determined using Israeli and US reference values. Results: BMI values at the 95th centile increased monotonously over time in all age and sex categories. Between 1990 and 2000, 95th centile values increased by 12.7% and 11.8% among second-grade boys and girls, respectively. Among fifth-grade children, 95th centile values increased by 10.2% and 8.4%, respectively. Among second graders in 2000, 11.4% of both boys and girls exceeded the BMI value recorded at the 95th centile in 1990. Among fifth-graders in 2000, 10.7% of boys and 11.1% of girls exceeded the 1990 BMI reference value (p for all comparisons < 0.001). The proportion of obese children increased over time using both Israeli and US reference values. Conclusion: This substantial increase in childhood obesity poses a serious health threat, and requires implementation of suitable public health interventions.