Purpose There is substantial concern surrounding affordability of orally administered anticancer therapies, particularly for Medicare beneficiaries. We examined rates of initiation and adherence to tyrosine kinase inhibitors (TKIs) among Medicare beneficiaries with chronic myeloid leukemia (CML) with and without cost-sharing subsidies. We selected TKIs given their effectiveness and strong indication for use among patients diagnosed with CML. Patients and Methods Using SEER-Medicare data, we identified individuals diagnosed with CML from 2007 to 2011. We used Cox proportional hazards regression to assess time from diagnosis to TKI initiation. We used generalized estimating equations to examine treatment initiation within 180 days and TKI adherence among initiators. We defined adherence as at least 80% of days covered during the 6 months after TKI initiation. Results Among 393 individuals diagnosed with CML from 2007 to 2011, 68% initiated TKI treatment within 180 days after diagnosis. In multivariate analysis, individuals with cost-sharing subsidies, younger age, lower comorbidity, and later year of diagnosis were significantly more likely to initiate TKIs. Among TKI initiators, 61% were adherent; adherence was lower for individuals age 80 years or older versus 66 to 69 years. Conclusion Only 68% of Medicare beneficiaries with CML initiated TKI therapy within 6 months of diagnosis. Delayed initiation among individuals without cost-sharing subsidies suggests that out-of-pocket costs may be a barrier to timely initiation of therapy among individuals diagnosed with CML.