Wolf-Hirschhorn syndrome (WHS) with partial deletion of the short arm of chromosome 4 has been exceptionally diagnosed in fetuses. We report prenatal diagnosis of five cases of monosomy 4p. The fetuses were karyotyped for severe intrauterine growth retardation (IUGR) diagnosed on routine ultrasound (US). In addition, cleft-lip and palate and diaphragmatic hernia respectively were found in two cases. The quantity of amniotic fluid was normal in all cases. At autopsy, the fetuses showed the typical craniofacial dysmorphy but without microcephaly. Major renal hypoplasia was the only constant visceral anomaly. Midline fusion defects were observed in all the fetuses, ranging from minor abnormalities such as scalp defect, hypertelorism, pulmonary isomerism, common mesentery, hypospadias and sacral dimple, to cleft palate, corpus callosum agenesis, ventricular septal defect, and diaphragmatic hernia. On post-mortem X-rays, a delayed bone age was always observed. All the placentae were hypotrophic, and two exhibited vascular lesions, although there was no maternal hypertension. Chromosomal studies showed that the breakpoints were within the 4p16 band in three cases, the 4p15 band in one case, and the 4p14 band in one case. The deletion was de novo in four cases, and resulted from a paternal translocation in one case. This study emphasizes the importance of karyotyping all fetuses with IUGR, especially when the quantity of amniotic fluid is normal, and suggests the possibility of recognizing on US the particular phenotype of WHS in utero.