BACKGROUND High-quality care must be not only appropriate but also timely. We assessed time to initiation of adjuvant chemotherapy for breast cancer as well as factors associated with delay to help identify targets for future efforts to reduce unnecessary delays. METHODS Using data from the National Comprehensive Cancer Network (NCCN) Outcomes Database, we assessed the time from pathological diagnosis to initiation of chemotherapy (TTC) among 6622 women with stage I to stage III breast cancer diagnosed from 2003 through 2009 and treated with adjuvant chemotherapy in nine NCCN centers. Multivariable models were constructed to examine factors associated with TTC. All statistical tests were two-sided. RESULTS Mean TTC was 12.0 weeks overall and increased over the study period. A number of factors were associated with a longer TTC. The largest effects were associated with therapeutic factors, including immediate postmastectomy reconstruction (2.7 weeks; P < .001), re-excision (2.1 weeks; P < .001), and use of the 21-gene reverse-transcription polymerase chain reaction assay (2.2 weeks; P < .001). In comparison with white women, a longer TTC was observed among black (1.5 weeks; P < .001) and Hispanic (0.8 weeks; P < .001) women. For black women, the observed disparity was greater among women who transferred their care to the NCCN center after diagnosis (P (interaction) = .008) and among women with Medicare vs commercial insurance (P (interaction) < .001). CONCLUSIONS Most observed variation in TTC was related to use of appropriate therapeutic interventions. This suggests the importance of targeted efforts to minimize potentially preventable causes of delay, including inefficient transfers in care or prolonged appointment wait times.