This chapter reviews prevention, including genetic counseling. It discusses genetic testing for diagnosis as opposed to screening and the treatment for genetic disease. Methods of prevention begin with education of the public and health care professionals and identification of those at risk. Genetic counseling is the process of helping people understand and adapt to the medical, psychological, and familial implications of genetic contributions to disease. The malignant cells often exhibit aneuploidy as well as translocations that are found only within the tumor cells. Genetic errors that arise from specific cell lines are somatic mutations. It is suggested that there is a thorough collection of family, genetic, and medical history for children entering the adoption process. Nurses may play a variety of roles in genetic counseling that reflect their preparation, area of practice, primary functions, and setting. The chapter explains the incidence of chromosome abnormalities.