A newborn male with a large diaphragmatic hernia presented in severe respiratory distress. Additional features included a paucity of subcutaneous tissue, mild facial dysmorphism, webbing of the neck, genital hypoplasia, and flexion contractures of the fingers. His karyotype showed a previously unreported de novo interstitial deletion of the long arm of chromosome 1 [46,XY,del(1)(pter----q32.3::q42.3----qter)]. Regional mapping of five human genes that have been provisionally assigned to chromosome 1 was performed by restriction analysis of genomic DNA from this patient. Glucocerebrosidase, H4 histone, renin, and alpha-spectrin genes mapped outside the deleted region, whereas an H subunit of the ferritin gene mapped to 1q32----q42. These results indicate the utility of chromosomal deletions in gene mapping, and the importance of karyotype analysis in newborns with diaphragmatic hernias.