The nutritional status of Brazilians has improved over the last three decades. Still, little is known about the role played by nutritional assistance programs that public institutions and philanthropic organizations provide for low-income preschool children, who face greater nutritional risk. Therefore, we carried out a quasi-experimental study to evaluate the nutritional impact of the municipal preschool nutritional assistance program in the city of Sorocaba, São Paulo, Brazil. Over the course of a year, we performed quarterly measurements of weight and height on 444 children, whose ages ranged from 3 months to 6 years. In this population, 164 children were assisted by the preschool nutritional program (intervention group), and 280 children were not (nonintervention group). The children in the nonintervention group were identified by a special census for that purpose; they did not attend the preschool but lived nearby. After obtaining informed consent and carrying out a pretest, professionals and university students interviewed the mothers of the participating children, following standard techniques and conditions. Anthropometric measurements were done by teams of two interviewers, one of whom was a permanent member of the team, using equipment calibrated by the appropriate regional technical organization. The correspondence between the first measurement and subsequent measurements was evaluated by stratifying the population into three groups by z scores for weight-for-age and for weight-for-height, using U.S. National Center for Health Statistics reference curves. The z score groupings were established at the beginning of the study for three different age groups: younger than 24 months, 24-36 months, and older than 36 months. The two study groups (intervention and nonintervention) were similar sociodemographically, with the following exceptions: maternal employment (more of the mothers of children in the intervention group had jobs outside the home); age (children in the intervention group were significantly older); nutritional status (it was worse in the intervention group); and prevalence of hospital admittance (it was higher in the intervention group). After just the first three months of the study, 32% of the children in the intervention group had moved to a higher nutritional stratum, whereas only 13% of children in the nonintervention group had shown improved nutritional status. The difference in favor of the intervention group increased with the length of the intervention and was higher among older children. These results show that the preschool nutritional assistance program helped to improve the assisted children's nutritional status.626-33