Chromosomal abnormalities can cause disability in children, and reproductive difficulty in parents. Many parents and couples seek genetic counseling in order to learn why they, or a relative, may have had a child with a particular collection of medical problems and/or intellectual disability. There may have been a history of multiple miscarriage, or infertility. They may want to know the outlook for a pregnancy, and what the risks might be. These and other questions concerning chromosome abnormalities are addressed in this standard text, which will be of interest to genetic counselors, medical geneticists, pediatricians and obstetricians, infertility specialists, and laboratory cytogeneticists. This third edition has been thorougly updated, and is richly illustrated and fully referenced. New chapters have been written on preimplantation diagnosis and on reproductive risks due to environmental agents. The practical applications of recent advances in molecular cytogentics are noted. The book will give counselors the information that will enable them to help concerned parents accommodate to their particular "chromosomal situation", and to determine what may be, for them, the best course of action.