During an 8-year period (1983-1991), blood karyotyping was performed in 235 fetuses with abdominal wall or gastro-intestinal tract defects. The overall incidence of chromosomal abnormalities was 29% (trisomy 21, n = 12; trisomy 18, n = 44; trisomy 13, n = 7; deletion of the short arm of chromosome 5, n = 1; unbalanced translocation involving chromosomes 4 and 15, n = 1; triploidy, n = 1; Klinefelter's syndrome, n = 1; and Beckwith-Wiedemann syndrome with mosaic duplication 11p15, n = 1). The karyotype was abnormal in 42 (36%) of the 116 fetuses with exomphalos, in none of the 26 with gastroschisis, in 10 (43%) of the 23 with duodenal atresia, in 18 (75%) of the 24 with lack of visible stomach, in 1 (4%) of the 24 with dilated bowel and in 2 (7%) of the 27 with echogenic hepatic nodules or abdominal cysts. Abnormal karyotypes were more commonly encountered when there was ultrasonographic evidence of multiple malformations (43%) compared to isolated defects (2%). Survival in fetuses with exomphalos (33%), absent stomach (4%), and large bowel obstruction (13%) was poor, whereas in those with gastroschisis (73%) or abdominal cysts (88%) survival was high; in small bowel obstruction and in duodenal atresia, survival was 65 and 57%, respectively.