Background: Melanoma is associated with significant risk of relapse after surgery. While the odds of relapse increase with advancing stage, long term relapse free survival (RFS) is possible without adjuvant therapy in a significant subset of patients as shown by AJCC v8 staging long term survival data. TI-ctDNA (Signatera™) is a non-invasive biomarker for MRD detection and functions by sequencing the patient’s own tumor for the creation of a customized panel of PCR probes based upon a tumor’s unique mutational profile. Positive TI-ctDNA testing is significantly associated with relapse after surgical resection in colorectal cancer and may help inform treatment decision-making, allowing for intensification or de-intensification of patient management. This study describes the operating characteristics of TI-ctDNA in monitoring for relapse in patients with resected melanoma. Methods: This is a single center retrospective analysis of patients with stage IIb-IV melanoma in surgical remission. Between January 2021 and January 2023, male and female patients presenting in surgical remission were monitored with TI-ctDNA at 6- or 12-week intervals. Surveillance imaging for relapse was performed according to standard of care guidelines appropriate for tumor stage. Patients were treated with immunotherapy, targeted therapy, or melanoma specific anti-tumor vaccine. Duration of RFS from surgery to detectable TI-ctDNA was recorded, along with duration of RFS from surgery to confirmed melanoma relapse. Results: 45 eligible patients were included in the analysis. 10 patients had detectable TI-ctDNA during the study period. 7 patients had confirmed relapse, 6 of whom were TI-ctDNA positive and 1 who was TI-ctDNA negative. The total relapse rate in TI-ctDNA positive patients (6/10) was significantly higher than the relapse rate in TI-ctDNA negative patients (1/35) [p = 0.0002]. Time to detection of positive TI-ctDNA was variable and ranged from 0 to 664 days (median 73 days). Conclusions: TI-ctDNA testing demonstrated preliminary ability to differentiate melanoma patients at the highest risk of relapse. Prospective evaluation of TI-ctDNA monitoring for determination of patients at high versus low risk of relapse is warranted and may help to inform future clinical trial designs by allowing for patient stratification to low risk (undetectable TI-ctDNA) and high risk (detectable TI-ctDNA) disease states.