Background: Controversy exists regarding the optimal surgical margin for cutaneous squamous cell carcinoma (cSCC). Current NCCN Guidelines recommend excision with a 4–6-mm clinical margin for low-risk cSCC and wider ( > 6-mm) clinical margin for high-risk cSCC tumors. However, adherence to this guideline is often difficult, as high-risk cSCCs frequently occur on the faces of elderly patients. Thus, we aim to investigate the correlation between different surgical margins and prognosis in patients with cSCC. Methods: Patients with cSCC who had undergone surgical excision of the primary site between 2011 and 2019 at 11 Japanese institutions were included in this study. Patients were divided into two groups: the standard margin group (SMG) with excisions adhering to the guideline-recommended margins, and narrower margin group (NMG) with excisions with narrower margins than are guideline-recommended. Local recurrence-free survival (LRFS), relapse-free survival (RFS), and overall survival (OS) were estimated using Kaplan–Meier analysis and compared between the two groups. Results: A total of 1204 patients with cSCC (SMG, 637; NMG, 567) were included in this study. RFS was significantly lower in SMG than in NMG (5-year RFS 72% vs 79%; P = 0.03); however, no statistically significant differences were observed between the two groups in LRFS (5-year LRFS 80% vs 82%; P = 0.41) or OS (5-year OS 84% vs 83%; P = 0.90). Due to striking statistical significance in several characteristics of patients between the two groups, subgroup analyses, focusing on the cohort of head and neck cSCCs, were also performed. The patient characteristics were similar between SMG and NMG in both the T1-sized tumor ( < 2 cm, SMG, 182; NMG, 250) and T2-sized tumor (2 cm ≤ tumor < 4 cm, SMG, 130; NMG, 136) cohorts, based on AJCC-TNM staging (8th edition). There were also no significant differences between the SMG and NMG in LRFS (5-year LRFS, T1: 80% vs 86%; P = 0.59; T2: 85% vs 84%; P = 0.84), RFS (5-year RFS, T1: 80% vs 81%; P = 0.84; T2: 77% vs 76%; P = 0.99), or OS (5-year OS, T1: 82% vs 87%; P = 0.42; T2: 88% vs 85%; P = 0.68). Furthermore, when the NMG was divided into the two margin groups (margins reduced by < 3 mm or ≥3 mm from the standard margin), no significant difference was observed in LRFS, RFS, and OS. Conclusions: This study did not reveal a significant impact of the size of clinical excision margins on survival in patients with cSCCs. Strikingly, the narrower margins may be more appropriate for < 4 cm-sized head and neck cSCCs.