The aim of this study was to evaluate the quality of prenatal care offered in 12 Basic Health Units (BHU) in the city of Sao Paulo, Brazil, through a review of medical and nurse charts, before and after the municipalization of the public health system. The indicator used considered excellence in care as: starting prenatal care in the first quarter of pregnancy; at least six medical visits; at least two results of blood screening for syphilis and one for HIV; returning to BHU up to 42 days after delivery. This indicator was not present in any care delivered in 2000, and only 7.7% of the care delivered in 2004 obtained it (1.1% to 30% of the care per unit assessed). Although there was an evident improvement in care during the period, the low proportion of excellent prenatal care shows an urgent need to improve this care in the BHU of São Paulo city.