To document overweight and underweight state-specific prevalence and examine trends among 2- through 4-year-old children from low-income families. State-specific and overall overweight and underweight prevalence for 1989, 1994, and 2000 and trend analyses during the study period are documented. Overweight was defined as a sex-specific body mass index (BMI) for age in the 95th percentile or higher and underweight as a sex-specific BMI for age in less than the fifth percentile on the 2000 Centers for Disease Control and Prevention (CDC) growth charts. These analyses are based on one randomly selected record per child per year for 30 states consistently participating in the CDC Pediatric Nutrition Surveillance System in 1989, 1994, and 2000. Prevalence in 1989 and 1994 is adjusted to state-specific age and race/ethnicity distribution of the population in 2000. Overweight and underweight prevalence were categorized as 5% or less, more than 5% to 10%, more than 10% to 15%, more than 15% to 20%, and more than 20%. The number of states that reported overweight prevalence of more than 10% increased from 11 in 1989 to 28 in 2000. Underweight decreased during the study period: 9 states in 1989 and 23 states in 2000 had a prevalence of 5% or less. No geographic predominance was apparent. Trend analyses showed significant increases in overweight in 30 states (P < .01) and decreases in underweight in 26 states (P < .05). Overweight is increasing and underweight is decreasing in our study population. We need to expand prevention and intervention efforts to reverse the rising trend of overweight in the United States.