BACKGROUND This study clarified the clinical results of locally advanced squamous cell carcinoma of the maxillary sinus (SCC-MS) that was treated with chemoradioselection using superselective intra-arterial cisplatin and concomitant radiation (RADPLAT). Prognostic factors were also investigated. METHODS We retrospectively analyzed 63 locally advanced SCC-MS patients treated with initial RADPLAT followed by sequential RADPLAT (S-RADPLAT) or surgery. RESULTS The 5-year progression-free survival (PFS) and overall survival (OS) rates of patients with T3, T4a, or T4b disease were 72.2%, 46.6%, and 33.3% (p = 0.104) and 83.3%, 51.6%, and 33.3% (p = 0.031), respectively. The 5-year PFS and OS rates of the S-RADPLAT or surgery groups with T4 disease were 39.6% and 60.6% (p = 0.199) and 44.7% and 63.3% (p = 0.276), respectively. Tumor extension into the medial and/or lateral pterygoid muscle (p < 0.001) and N classification (p = 0.012) were considered significant factors for PFS. Regarding OS, tumor extension into the medial and/or lateral pterygoid muscle (p = 0.005) was considered a statistically significant risk factor. CONCLUSIONS It may be better for T4 non-responders to initial RADPLAT to undergo surgery. Patients with high risk factors of positive neck metastasis or pterygoid muscle extension may need adjuvant chemotherapy.