We report the use of fluorescent in situ hybridization (FISH) with a DNA library of chromosome 1-specific probes to confirm the karyotype, 46,XY,15+der15,t(1;15)(q32.1; q26.3), obtained by prenatal periumbilical blood sampling from a fetus who exhibited multiple abnormalities by ultrasound examination. GTG-banding of chromosomes obtained from the mother showed a normal karyotype, while the father was unavailable for study. The propositus was born at 37 weeks gestation and survived for several weeks. Cytogenetic analysis performed after the birth of the male infant with multiple anomalies verified partial trisomy 1q. This patient is compared with other partial trisomy 1q patients reported in the literature. The usefulness of FISH is demonstrated in situations where fetal abnormalities are present with de novo chromosomal rearrangements where paternal chromosomes are unavailable for study.