Objective: Placental mosaicism for a subset of a chromosome, a structural chromosomal aberration, is thought to be a very rare finding in chorionic villus samples. Here, we present clinical and laboratory data on five cases with such mosaicism for structural chromosomal aberrations. Methods: During a period of 6 months, chromosomal microarray was carried out on DNA extracted from 100 uncultured chorion villous samples from high-risk pregnancies. Results: In five of 100 consecutively collected samples (5/100), mosaicism for a structural chromosomal aberration was detected. The mosaic aberration was subsequently detected in fetal tissue in three of the five cases. Conclusion: Chromosomal microarray can detect placental mosaicism for structural chromosomal aberrations. This kind of mosaicism may be more frequent than previously anticipated, and the fetal involvement seems difficult to predict. These findings highlight the complexity of mosaicism for structural chromosomal aberrations in prenatal samples in the chromosomal microarray era.