A case of familial heterozygous pericentric inversion of chromosome 1 [inv(1)(p13q23)] is presented. The inversion was incidentally detected in a fetus whose mother received prenatal chromosomal diagnosis due to her age (40 years old), and thereafter the same inversion was detected in the father whose phenotype was normal. No abnormalities were found in the phenotype of the newborn carrier. Semen analysis of the father revealed normal findings. The couple had no history of spontaneous abortion.