We examined differences in time to diagnosis by race/ethnicity, the relationship between time to diagnosis and stage, and the extent to which it explains differences in stage at diagnosis across racial/ethnic groups. Our analytic sample includes 21,427 non-Hispanic White (White), Hispanic, non-Hispanic Black (Black) and non-Hispanic Asian/Pacific Islander (Asian) women diagnosed with stage I to IV breast cancer between January 1, 2000 and December 31, 2007 at one of eight National Comprehensive Cancer Network centers. We measured time from initial abnormal mammogram or symptom to breast cancer diagnosis. Stage was classified using AJCC criteria. Initial sign of breast cancer modified the association between race/ethnicity and time to diagnosis. Among symptomatic women, median time to diagnosis ranged from 36 days among Whites to 53.6 for Blacks. Among women with abnormal mammograms, median time to diagnosis ranged from 21 days among Whites to 29 for Blacks. Blacks had the highest proportion (26 %) of Stage III or IV tumors. After accounting for time to diagnosis, the observed increased risk of stage III/IV breast cancer was reduced from 40 to 28 % among Hispanics and from 113 to 100 % among Blacks, but estimates remained statistically significant. We were unable to fully account for the higher proportion of late-stage tumors among Blacks. Blacks and Hispanics experienced longer time to diagnosis than Whites, and Blacks were more likely to be diagnosed with late-stage tumors. Longer time to diagnosis did not fully explain differences in stage between racial/ethnicity groups.