Chromosomal abnormalities can cause disability in children, and reproductive difficulty in parents. Many parents and couples seek genetic counselling 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 counsellors, medical geneticists, paediatricians and obstetricians, infertility specialists, and laboratory cytogeneticists. This third edition has been thoroughly updated, and is richly illustrated and fully referenced. New chapters have been written on preimplantation diagnosis and recent advances in molecular cytogenetics are noted. The book will give counsellors 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.