OBJECTIVE This study was undertaken to validate the prediction of 24- hour urine protein excretion by a single voided urine protein-to-creatinine (P:C) ratio in a hospitalized pregnant population at our institution. We sought to evaluate the ability of serial single voided P:C ratios to follow the course of proteinuria. METHODS Pregnant patients who were admitted to the antepartum unit at Northwestern Memorial Hospital and who were undergoing a 24-hour urine collection for the quantitation of proteinuria were recruited. A single voided urine specimen was obtained after the completion of the 24-hour urine collection and analyzed for the P:C ratio. RESULTS Thirty patients completed the study. There was a significant correlation between the 24-hour urine protein and the P:C ratio (r = 0.93, P <.001). The associations of maternal age and gestational age at collection with P:C ratio and 24-hour urine protein were weak and not significant. There was a nonsignificant trend of higher P:C ratios and 24-hour urine protein in nulliparous patients compared with multiparous patients. On the basis of multiple linear regression, there was no confounding effect of maternal age, gestational age, or parity. Eight patients had serial paired urine collections performed. In all of the cases, the trend of increasing or decreasing 24-hour urine protein excretion was predicted by the P:C ratio. CONCLUSIONS Our data support the use of single voided P:C ratio in hospitalized pregnant patients to predict the 24-hour urine result. In addition, the P:C ratio appears to predict trends in protein excretion over time.