This study compares socio-demographic factors, mothers' biological characteristics, and quality of care at maternity hospitals in the City of Rio de Janeiro, Brazil. A sample of 10,072 post-partum women in 47 hospitals was selected. Data were collected by interviewing mothers in the immediate post-partum and from medical records. The chi2 test was used to analyze homogeneity of ratios. Significant differences were found between patients in public and private hospitals in relation to family support, healthy habits during pregnancy, reproductive history, access to and satisfaction with prenatal care and delivery, and particularly adverse effects in the newborns. Private maternity hospitals showed better results, although they displayed excessive cesarean and neonatal inter-hospital transfer rates. The stratum consisting of public Federal and State maternity hospitals received women with greater morbidity, had lower neonatal transfer rates, and received a more positive assessment by clients of the Unified National Health System (SUS). Private maternity centers contracted out by the SUS were the ones that most refused treatment to patients, leading to delays in patient care for delivery.