Background:The protein:creatinine ratio in random, untimed urine samples correlates with 24-h protein excretion in pregnant women with and without hypertension. Nevertheless, whether this ratio is appropriate as a screening test for proteinuria is still unclear, in part because of the paucity of large studies. Methods: We measured protein:creatinine ratios in random urine samples and protein contents of 24-h urine samples in a cross-sectional study of 927 hospitalized pregnant women at >20-weeks of gestational age and in a 2nd cohort of 161 pregnant women. In the 2nd group, urine specimens were obtained before and after completion of the 24-h collections, avoiding 1st-morning void specimens. Results: Protein excretion was >300 mg/24 h in 282 patients (30.4%). The urine protein:creatinine ratio and the 24-h protein excretion were significantly correlated (r ‫؍‬ 0.98, P <0.001). The protein:creatinine ratio as an indicator of protein excretion >300 mg/24 h was >0.3. The sensitivity and specificity were 98.2% and 98.8%, respectively. Positive and negative predictive values were 97.2% and 99.2%, respectively, and positive and negative likelihood ratios were 79.2 and 0.02, respectively. The diagnostic accuracy of the urinary protein: creatinine ratio was corroborated in the 2nd cohort of patients, which also showed no statistically significant