Background: Anti-tumor lymphocytes activated in response to ICIs may cross the blood brain barrier with effect on brain metastases (BM). Preliminary evidence suggests that ICIs alone are effective for melanoma BMs. However, the ability of ICI to effectively control NSCLC BMs without radiotherapy is controversial. By comparing serial MRIs and patterns of progression in ICI and chemotherapy treated patients, we sought to investigate the role of ICI in BM control in NSCLC patients. Methods: Serial MRIs were reviewed in ICI treated NSCLC patients with known BMs. Eligible patients must have a minimum of one baseline MRI and a follow-up within 3 months of CNS directed treatment. Patients with EGFR/ALK mutations were excluded. A control cohort of patients who had never received ICIs was selected using the same criteria. The primary outcome was cumulative CNS progression and intracranial progression free survival (iPFS) analyzed using an accelerated failure time model and competing risk analysis. Results: We identified 137 ICI treated NSCLC patients with known BMs. After excluding for patients without serial MRIs, we analyzed 40 ICI treated patients and 39 controls. All patients received upfront radiotherapy or surgery and the modality used was similar (p = 0.13). CNS failure was less common in the ICI group (p = 0.02). ICI treated patients had a trend to longer iPFS in the PD-L1 ≥50% subgroup (p = 0.058). Cumulative incidence of progressive BM at 12 and 24 months were significantly lower in the ICI treated PD-L1 ≥50% subgroup: 19%/19% vs 50%/56% (p = 0.02). Patients in the PD-L1 ≥50% subgroup who achieved a systemic partial response (n = 10) did not experience any CNS events despite extracranial progression in some. Conclusions: Durable CNS disease control is observed with ICIs in NSCLC with PD-L1 ≥50% and demonstrates a high level of concordance with systemic response. The need for radiotherapy in PD-L1 ≥50% disease should be investigated and may be reasonably delayed in asymptomatic patients with small BMs. Importantly, the same trend was not observed in PDL1 < 50% patients and caution is needed in employing this strategy in this subset of patients.