Breast cancer remains the most common cancer in women, and screening mammography is the best method for early detection. Approximately 10% to 15% of women undergoing screening mammography have abnormal or incomplete findings that require further diagnostic studies. The time to follow up is reported to be between 9 weeks and more than 19 weeks. Evidence indicates that a delay of more than 3 months in women with symptomatic breast cancer is associated with increased rates of breast cancer recurrence and death. The reasons for the delay are varied, and study findings suggest that minority and low-income women experience more delays than other groups do. The results from 22 studies are summarized. The identified barriers to completion of screening mammography were grouped as patient, provider, and system categories. Most of the studies were descriptive, retrospective studies that describe and measure the barriers in varied ways. Patient barriers were the most extensively described barrier, with little attention given to specific provider and system barriers. Women of nonwhite race with lack of insurance emerged as a subgroup that experienced more delay after abnormal or incomplete results. Provider and system barriers are also not well documented, and further exploration of these barriers is also recommended.