Objective: The aim of this study was to compare 3-dimensional (3D) lung volume measurements with 2-dimensional (2D) biometric parameters in predicting pulmonary hypoplasia in complicated pregnancies. Study Design: In this prospective study, 1-4 scans of the fetal lungs were obtained in 33 pregnancies complicated by various disorders or complications with regard to pulmonary hypoplasia. The 3D lung volumes vs gestational age or estimated fetal weight, the thoracic circumference vs gestational age or femur length, the thoracic/abdominal circumference ratio, and the thoracic/heart area ratio were measured. Results: Of the 33 infants, 16 (48.5 %) were diagnosed with pulmonary hypoplasia on postmortem examination or the clinical and radiological presentation. Three dimensional lung volume measurements had a better diagnostic accuracy for predicting pulmonary hypoplasia (sensitivity, 94%; specificity, 82%; positive predictive value [PPV], 83%; negative predictive value [NPV], 93%), compared with the best 2D biometric measurement thoracic/heart area ratio (sensitivity, 94%; specificity, 47%; PPV, 63%; NPV, 89%). Conclusion: 3D lung volume measurements seem to be useful in predicting pulmonary hypoplasia prenatally. © 2008 Mosby, Inc. All rights reserved.