The effect of severe oligohydramnios (due to prolonged premature rupture of the membranes (PROM)) on breathing movements and lung development was studied longitudinally in 11 human fetuses. Prenatally, fetal breathing movements (FBM) were scored off-line from weekly, 1 h during ultrasound recordings (n = 47). In each recording, the incidence of FBM was scored according to 4 different methods. Postnatally, the cases were retrospectively assigned to a group with normal (n = 4), partially hypoplastic (n = 3), or hypoplastic (n = 4) lungs. Compared to control fetuses, the percentage of time spent breathing (%FBM) was low (2-5%) and did not increase with gestational age. Large inter-individual and intra-individual variations in the %FBM were found in all 3 diagnostic groups. Evaluation of the %FBM according to the 4 different methods revealed no significant differences between the 3 groups. We conclude that lung development is, at least partly, independent of the incidence of FBM. Furthermore, the analysis of FBM cannot reliably predict lung development in fetuses with oligohydramnios due to PROM.