Importance: Breast cancer in women between the ages of 15 and 39 years (adolescents and young adults [AYAs]) constitutes 5% to 6% of all breast cancer cases in the United States. Breast cancer in AYA women has a worse prognosis than in older women. Five-year survival rates are lowest for AYA women, and only a few studies have examined the impact of delay in treatment, race/ethnicity, and other socioeconomic factors on survival in AYA women. Objective: To examine the impact of treatment delay time (TDT), race/ethnicity, socioeconomic status, insurance status, cancer stage, and age on the survival from breast cancer among AYA women. Design, Setting, and Participants: This is a retrospective case-only study of 8860 AYA breast cancer cases diagnosed from 1997 to 2006 using the California Cancer Registry database. Exposure: Treatment delay time was defined as the number of weeks between the date of diagnosis and date of definitive treatment. Kaplan-Meier estimation was used to generate survival curves, and a multivariate Cox proportional hazards regression model was performed to assess the association of TDT with survival while accounting for covariates (age, race/ethnicity, socioeconomic status, insurance status, cancer stage [American Joint Committee on Cancer], tumor markers, and treatment). Main Outcomes and Measures: Five-year survival rates for breast cancer as influenced by host factors, tumor factors, and TDT. Results: Treatment delay time more than 6 weeks after diagnosis was significantly different (P<.001) between racial/ethnic groups (Hispanic, 15.3% and African American, 15.3% compared with non-Hispanic white, 8.1%). Women with public or no insurance (17.8%) compared with those with private insurance (9.5%) and women with low socioeconomic status (17.5%) compared with those with high socioeconomic status (7.7%) were shown to have TDT more than 6 weeks. The 5-year survival in women who were treated by surgery and had TDT more than 6 weeks was 80% compared with 90% (P=.005) in those with TDT less than 2 weeks. In multivariate analysis, longer TDT, estrogen receptor negative status, having public or no insurance, and late cancer stage were significant risk factors for shorter survival. Conclusions and Relevance: Young women with breast cancer with a longer TDT have significantly decreased survival time compared with those with a shorter TDT. This adverse impact on survival was more pronounced in African American women, those with public or no insurance, and those with low SES.