OBJECTIVE To compare the lamellar body number density (LBND) count in amniotic fluid using the fluorescent polarization (FP) test as a diagnostic parameter for the assessment of fetal pulmonary maturity. METHODS This was an analytical, controlled cross-sectional study conducted on 60 pregnant women from March 2002 to December 2007. Amniotic fluid specimens were obtained by amniocentesis or at the time of caesarean section, and submitted to the LBND and FP tests (TDxFLM, Abbott Laboratories), the latter considered to be a reference test, and compared in terms of the presence or absence of respiratory distress syndrome (RDS). Cut-off values for maturity were established at 30,000 lamellar bodies/microL for the LBND test and 55 mg/g albumin for the FP test. Maternal and perinatal characteristics and neonatal evolution were evaluated, and the performance of the diagnostic tests regarding fetal pulmonary maturity was determined. In the statistical analysis, descriptive measures were used and the sensitivity, specificity and positive and predictive values of the tests were determined with the level of significance set at p<0.05. RESULTS Maternal age ranged from 15 to 34 years (mean: 26.6 years) and gestational age ranged from 24.3 to 41.6 weeks (mean: 35.1 weeks). RDS was diagnosed in 35.1% of neonates. Perinatal characteristics such as weight, Apgar score, and RDS incidence were compared to the results of the LBND and FP tests and a significant correspondence (p<0.05) was observed between the groups of neonates clinically classified as mature and immature in both tests. The tests were concordant in 68.3% of the cases. Comparison of the PF and LBND tests revealed 100% specificity for both and a higher specificity for the LBND test (73.1% as opposed to 51.9% for the PF test). The gold standard for the determination of fetal maturity is the occurrence of RDS. The positive predictive value of the LBND test was higher (36.4%) than that of the FP test (24.2%) (p<0.05) and the negative predictive value was 100% for both tests. CONCLUSIONS The present study demonstrated that the LBND test has 100% sensitivity and higher specificity than the reference test (FP). In addition, the LBND test is considered to be rapid, accessible, inexpensive and feasible for the Brazilian reality, and it can be used as a reliable test for the prediction of fetal pulmonary maturity.