Background: Molecular monitoring every 3 months using quantitative polymerase chain reaction (qPCR) of BCR-ABL mRNA transcripts on International Scale is recommended by the National Comprehensive Cancer Network and the European LeukemiaNet for patients (pts) in chronic phase of CML. A previous study has shown an underutilization of qPCR in the community setting. This study assessed the impact of the frequency of molecular monitoring on hospitalization and medical costs among CML pts receiving 1^st-line tyrosine kinase inhibitor (TKI) therapies. Methods: Two U.S. administrative claims databases were combined (01/2000-06/2012) to identify adult CML pts initiated on TKIs (imatinib, dasatinib, nilotinib). Pts were followed for 12 months from their first TKI prescription and categorized into 3 cohorts based on frequency of qPCR tests (i.e., 0, 1-2, and 3-4). Number of inpatient admissions and medical service costs (measured from a US payer perspective; adjusted to 2012 U.S. dollars) were compared between cohorts. Multivariate regression models adjusted for confounding factors (e.g., age, gender, CML complexity, TKI). Results: The study included 1,205 CML pts. Over the 12-month study period, 41.0% of the pts had no qPCR test, 31.9% had 1-2 tests, and 27.1 % had 3-4 tests. Compared to pts with no qPCR monitoring, those with 3-4 tests incurred 37% fewer CML-related (i.e., a primary CML diagnosis) inpatient admissions (p=.017) during the study period, leading to a $4,000 (p=.009) reduction in CML-related inpatient costs and $5,663 (p=.005) reduction in all-cause inpatient costs, accounting for the majority of the $5,997 reduction in total medical service costs (p=.049). Pts with 1-2 tests a year showed smaller and statistically insignificant reductions from those with no test in the frequency of hospitalization and medical costs. Conclusions: Among CML pts who initiated 1^st-line TKIs, pts with 3-4 qPCR tests a year incurred fewer inpatient admissions and lower medical service costs compared to pts with no test. These findings suggest that pts would benefit from regular qPCR testing and underscore the value of molecular monitoring in the delivery of quality care for Ph+ CML-CP pts on TKI therapies.