Cytogenetic analysis after conventional staining and Q-banding demonstrated a pericentric inversion of chromosome 14 in the mother of a child with a mental retardation/multiple congenital abnormality syndrome and an abnormal chromosome 14. The proposita's partial duplication for the distal segment of 14q is apprently the result of crossing over within the inverted segment during meiosis. An attempt is made at assessing the risk that a carrier of the described pericentric inversion faces of having an abnormal child. The estimate of the risk depends on two factors: 1) the probability of a crossover occurring within the inverted segment during meiosis, and 2) the probability of a child with either of the two possible unbalanced recombinant chromosomes being born alive. An explanation is offered as to why some pericentric inversions confer a signifcant risk while others are so benign and occur with such a high frequency that they can be considered normal chromosomal variants, rather than chromosome aberrations.