Laryngeal anterior commissure (AC) cancer has been the subject of much controversy. Our study was aimed at pathologically evaluating the tendency of AC cancer to invade the thyroid cartilage and analyzing the role of thyroid cartilage invasion by tumor cells at the AC as an anatomic cause for irradiation failure. Our study included 36 patients with glottic cancer involving AC. Patients with recurrent or persistent disease after radiotherapy underwent salvage surgery. Surgical specimens from 22 patients who had open surgery, either as primary or salvage surgery, were available for pathologic examination to identify the presence of cartilage invasion. We found microscopic invasion of the thyroid cartilage in 40.9% of the studied tumors. Only 21.4% of patients who had open salvage surgery showed evidence of cartilage invasion at the AC. We concluded that laryngeal AC cancers are more likely to invade the cartilage, and that anatomic risk factors are not the main cause of irradiation failure.