OBJECTIVES: To examine real world health care utilization (HCU) and costs associated with whole brain radiation therapy (WBRT) or stereotactic radiosurgery (SRS) as the initial or only treatment of brain metastasis (BrMets). METHODS: A retrospective longitudinal analysis utilized claims data from a national health insurer, identifying patients ≥18 yrs with  ≥2 claims ≥7 days apart for BrMets (ICD-9 198.3x) from  1/2004-4/2010.  The index date was first BrMts claim date.  Pre-index period of ≥6 months and ≥1 month post-index enrollment (<1 month was permitted if due to death). Patients with primary brain cancers were excluded.  HCU and all-cause per-patient per-month (PPPM) costs were examined. RESULTS: The study included 1,901 and 303 patients who received WBRT or SRS as first or only treatment, with 179d vs. 306d follow-up, respectively. Baseline Charlson comorbidity scores were similar. Mean age at BrMets diagnosis was higher for WBRT (59yrs) vs. SRS (57yr) [p-value=0.002].   Rates of HCU (events/person-month) were higher among WBRT vs. SRS patients for office visits (5.29 vs. 3.69), ER visits (0.25 vs. 0.17), and inpatient stays (0.26 vs. 0.17); rates of outpatient visits were lower among WBRT patients (2.31 vs. 3.24) [p-value<0.001]. Total costs PPPM were higher for the SRS ($20,682) vs. WBRT cohort ($16,909) [p-value=0.005].  Outpatient costs PPPM was the major cost-driver among the SRS cohort ($8,936, 43% of total) vs. $3,192 (19% of total) for WBRT.  Office costs PPPM contributed most to overall cost among WBRT ($3,428, 20% of total) vs. $3,053 (18% of total) for SRS.  Pharmacy costs PPPM were higher for the SRS ($1,232) vs. WBRT cohort ($692) [p-value <0.001]. CONCLUSIONS: BrMets patients with SRS incurred higher cost compared to WBRT patients. SRS is recommended for BrMets patients with ≤3 lesions and WBRT in >3 lesions may explain longer survival among SRS patients. Additional studies are augmented to understand differences.