Uterine fibroids, benign tumors of the uterus, are the most common female pelvic tumor. Fibroids are highly heterogeneous, with some women developing a single small fibroid while other women develop multiple and/or large fibroids. In addition, racial disparities in fibroid size and number support that fibroid characteristics have a genetic component. For example, African American (AA) women have more numerous and larger fibroids than European American (EA) women. Furthermore, AAs are two times more likely than EAs to receive surgical treatments for fibroids such as a hysterectomy. Unfortunately, most research on fibroids to date has not evaluated risk factors for specific fibroid characteristics. The purpose of this thesis is to provide a deeper understanding on both epidemiology and genetic risk factors of fibroid characteristics, fibroid number (single vs. multiple), volume of largest fibroid, and largest dimension of all fibroid measurements. After identifying epidemiologic risk factors for fibroid characteristics, this study identified several novel genetic loci associating with either fibroid size or number by methods of genome-wide association studies (GWAS) and admixture mapping studies. Lastly, this study estimated heritability of fibroids and fibroid size. Advisors/Committee Members: Bingshan Li (committee member), Melissa F. Wellons (committee member), Todd L. Edwards (committee member), Nancy J. Cox (committee member), Digna R. Velez Edwards (committee member), David C. Samuels (Committee Chair).