Background: Few studies have examined how patterns of care relate to clinical consensus guidelines for metastatic colorectal cancer (mCRC) in real-world settings. This study investigated treatment patterns around systemic therapies for older mCRC patients using SEER-Medicare data. Methods: We utilized data from a linkage of national Medicare claims data with records from the 12 Surveillance, Epidemiology, and End Results (SEER) regions for patients diagnosed with stage IV CRC between 2011 and 2014. Other inclusion criteria included adenocarcinoma histology, being > 65 years of age, and continuous Part A/B enrollment 12 months prior to diagnosis. We conducted bivariate analysis and multivariate modeling to evaluate the association between age, race, gender, SEER region, and comorbidity score with receipt of systemic therapy. We examined first and subsequent lines of therapy, and classified them as adherent or non-adherent to NCCN guidelines. Results: Of 102,461 CRC patients, 6,360 (6.2%) patients had evidence of metastatic disease and met all inclusion criteria. 3,155 (49.6%) received no systemic therapy. Of the 2,976 (46.8%) who received systemic therapy with identifiable regimens, FOLFOX/CAPOX was the most common 1L regimen (32.9%), followed by 5-FU or capecitabine alone (26.4%) – both identified as guideline-adherent therapies. Non-guideline adherent regimens (such as use of single-agent oxaliplatin or bevacizumab) were uncommon as 1L therapies (1.4%). 1,553 patients (52.2%) progressed to a 2L therapy, 715 (24.0%) progressed to a 3L therapy, and 320 (10.8%) to a 4L therapy. A large proportion of 2L (26.9%) and 3L (24.2%) treatments contained bevacizumab. 96 patients (3.2%) received regorafenib, representing 6.7% of 3L and 10.6% of 4L therapies. Patients who did not receive systemic therapy were older (mean age of 80.8 vs 74.9) and had multiple comorbidities (63.1% vs 48.4% with Klabunde score > 1). Conclusions: In a Medicare-insured mCRC cohort, patients generally received systemic therapy adhering to consensus guidelines. However, many patients did not receive systemic therapy – suggesting there may be delays in diagnosis and barriers to treatment which lower systemic therapy utilization.