We evaluated whether a correlation existed between fetal pulmonary magnetic resonance imaging (MRI) findings and postnatal mortality, as well as the requirements for extracorporeal membrane oxygenation (ECMO) in infants with prenatally diagnosed, isolated left-sided congenital diaphragmatic hernia (CDH). Twenty-one pregnant women carrying fetuses with CDH underwent 30 MRI scans, and the right-sided fetal lung volume (FLV) was measured. In the control, a regression analysis was performed to associate FLV with gestational age. This yielded a formula that enabled the calculation of the expected right fetal lung volume (ERFLV). In cases with CDH, the right-sided observed FLV/ERFLV (= %RFLV) was compared with both the postnatal mortality and whether ECMO was required. Additionally, we investigated the relationship between the lung shape on MRI (whether there was a complete pulmonary baseline present) and postnatal mortality. The %RFLV was significantly lower in nonsurvivors compared with survivors. Among survivors, the %RFLV was significantly lower in infants who required ECMO compared with those who did not. The pulmonary baseline was completely present in 3 (38%) and 13 (100%) of the nonsurvivors and survivors, respectively. In isolated left-sided CDH, the %RFLV is a good predictor not only of postnatal mortality but also of the requirement for ECMO.