Introduction The impact of cervical cancer on morbidity and mortality depends not only on the availability and coverage of screening, but also on the quality of the sample. The aim of this study was to evaluate the quality of Pap smear of the Primary Care Units (PCU), of São Paulo city, Brazil.

Methods This was a cross-sectional study. A sample of 478 Pap smears was selected from 12 PCU-São Paulo-Brazil, between April and September 2010. Collection date, name of the responsible physician, record number, age, pregnancy presence, and previous patient's collections, date of result, presence and epithelial classification of the sample and cytological result were collected from the “registration book”. The samples were classified as satisfactory with squamous columnar junction (SCJ), satisfactory without SCJ, and unsatisfactory. Samples without epithelial classification in the “registration book” were reported as “missing”. Descriptive analyses were calculated.

Results The mean age was 39 years (SD=14.2), median 37 years (range 14–82). 38.1% of samples were satisfactory with SCJ, 22.6% satisfactory without SCJ, 0.4% unsatisfactory and 38.9% missing.

Conclusion It is concluded that there was a low percentage of unsatisfactory samples; however, the results are unreliable, because a high percentage of samples without the epithelial classification was identified. It is necessary to improve the recording of the epithelia by professionals from PCU, because a low quality examination can lead to inadequate prevention of cervical cancer.