The recent literature on laryngeal surgical oncology has increasingly focused on the negative prognostic impact of neoplastic involvement of the posterior portion of the inferior paraglottic space, which we refer to as the “thyro-cricoarytenoid space” (TCAS). We retrospectively considered the prognostic significance of TCAS involvement in a cohort of 84 patients treated with open partial horizontal laryngectomy for glottic squamous cell carcinoma. Univariate analysis was conducted on the prognostic value of several clinical and pathological parameters. Cases with TCAS involvement experienced a higher recurrence rate and shorter disease-free survival. Neoplasms involving the TCAS should be considered and treated as extralaryngeal malignancies. Posterior glottic tumours with TCAS invasion have worse prognosis when managed with conservative surgery. Total laryngectomy should be considered in cases of locally-advanced glottic carcinoma with TCAS involvement.