In order to determine the frequency of associated malformations and chromosomal defects in patients with congenital diaphragmatic hernia (CDH) our experiences with CDH during the last 8 years (1985-1993) were reviewed. During the study period, 33 fetuses (prenatal group) with CDH were examined at our level III ultrasound department. In the same period 11 neonates (postnatal group) were admitted to our pediatric surgical unit after postnatal diagnosis of a CDH. Those cases had not been suspicious for CDH during prenatal level I scan. In 24 (72.7%) of the cases with CDH seen prenatally, at least one or more extradiaphragmatic malformations could be detected. Most of them affected the cardiovascular, skeletal, genitourinary and nervous system. Six (18.1%) fetuses had chromosomal abnormalities, especially trisomy 18. In contrast to these findings just 4 of the 11 babies (36.3%) seen postnatally had associated malformations and all of them had a normal chromosome set. Survival rate of fetuses with CDH and associated anomalies (7.1%) was poor, in contrast to those with an isolated CDH (43.7%). Prenatal ultrasound investigations being suspect for CDH should encourage the clinician to make further diagnostical efforts. This includes detailed ultrasound examination and cytogenetic analysis. Associated malformations as well as chromosomal defects are often present in affected patients.