Risk factors for pediatric hospitalization were studied using a cross-sectional multi-stage cluster sample survey. A standardized questionnaire was answered by children's mothers or other care providers. In the municipality of São Luís, Maranhão, Brazil, 596 children aged 1 to 4 years were sampled in 50 census tracts. Design effect was calculated for each estimate. Hospitalization rate was 24.4%. Main causes of hospitalization were pneumonia (7.3%) and diarrhea (7.1%). The Unified National Health System (SUS) and private insurance accounted for 78.1% and 18.2% of hospital admissions, respectively. After adjustment for confounding by Cox proportional hazards model modified for cross-sectional design, children whose families earned less than one minimum monthly wage and those with private insurance were at higher risk of hospitalization. Hospitalization due to outpatient-sensitive diseases accounted for most cases. The U-shaped hospitalization pattern suggests low quality of outpatient services among the poor and may be a proxy indicator for unnecessary and iatrogenic hospitalization among privately insured children.