To assess whether timing of initial post-diagnosis cancer care differs between American Indian and Alaska Native (AI/AN) and non-Hispanic White (NHW) patients, we accessed SEER-Medicare data for breast, colorectal, lung, and prostate cancers (2001-2007). Medicare claims data were examined for initiation of cancer-directed treatment. Overall, AI/ANs experienced longer median times to starting treatment than NHWs (45 and 39 days, p < .001) and lower rates of treatment initiation (HR[95%CI]: 0.86[0.79-0.93]). Differences were largest for prostate (HR: 0.80[0.71-0.89]) and smallest for breast cancer (HR: 0.96[0.83-1.11]). American Indians / Alaska Natives also had elevated odds of greater than 10 weeks between diagnosis and treatment compared with NHWs (OR[95% CI]: 1.37[1.16-1.63]), especially for prostate cancer (OR: 1.41[1.14-1.76]). Adjustment for comorbidity and socio-demographic factors attenuated associations except for prostate cancer. In this insured population, we observed evidence that AI/ANs start cancer therapy later than NHWs. The modest magnitude of delays suggests that they are unlikely to be a determinant of survival disparities.