Introduction: Prelabor rupture of membranes (PROM) is a frequent clinical situation, and the decision about the best time for delivery remains controversial, mainly due to the risk of neonatal respiratory morbidity (NRM). Assessment of fetal lung maturity using ultrasound, a safe method and widely used in current obstetrical practice, could change this scenario. This study was designed to evaluate the ability of quantitative ultrasound method QuantusFLM® to predict NRM in patients with PROM and whether maternal BMI, gestational age, occurrence of the disease, and presence of oligohydramnios influenced the performance. Methods: Patients with singleton gestations, diagnosis of PROM, and gestational age between 24 and 38 weeks and 6 days were included. Fetal lung image was acquired by ultrasound within 48 h prior to delivery and analyzed by QuantusFLM®. The results were then paired with neonatal outcomes to assess the program’s ability to predict the NRM in this specific group. A logistic regression model was created to analyze factors that could affect the test results. Results: Fifty-four patients were included. Mean maternal BMI was 28.99 kg/m<sup>2</sup>, and in 25 patients (46.2%), oligohydramnios was observed at the time of examination. Mean gestational age at delivery was 35 weeks and 4 days, and the NRM prevalence was of 18.5%. QuantusFLM® predicted NRM with a 60% sensitivity, 79.5% specificity, 40% positive predictive value, 89.7% negative predictive value, and 75.6% accuracy. Maternal BMI, disease occurrence, presence of oligohydramnios, and gestational age did not interfere with the evaluation. Conclusion: This study demonstrates a good accuracy of QuantusFLM® as a NRM predictor in patients with PROM, with particular reliability in identifying that pulmonary maturity has already occurred.