For many years women have been under-represented in mathematics and related careers. Many women have been successful at the undergraduate level in a mathematics major, yet chose other career paths. In this study seventeen women, all of whom had done well in mathematics and have either graduated with an undergraduate degree in mathematics or had a career in mathematics, were interviewed about their experiences and perceptions as to why women stay in or leave mathematics. Some of reasons the women reported include the following: they did well in mathematics early in school years, they had encouragement from family and teachers, they had role models and were shown positive attitudes towards women in mathematics, they saw mathematics as a great opportunity for a job in the future, and they were given funding. Some of the reasons the women had left included the following: they had a negative experience, they saw more opportunities elsewhere, their job required another type of degree, or they lost interest in mathematics. More needs to be done to attract women to mathematics and to raise awareness of women's experiences in mathematics. In addition to describing women's experiences, this study offers suggestions for practice (including recommendations for parents, teachers, and institutions) and discusses implications for future research. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]