Introduction Advanced techniques of radiotherapy have decreased the late complication rate to < 1% at the larynx. Cartilage necrosis is one of rare toxicities associated with radiotherapy. Case presentation We present the case of post-irradiation thyroid cartilage necrosis in an adult patient with glottic cancer. The radiotherapy was performed 3 weeks after primary surgery using CO2 laser (hemi-laryngectomy, neck dissection). The cancer region and bilateral lymph nodes were exposed to a daily fraction of 1.8 Gy up to a total dose of 59.4 Gy in IMRT technique. 5.5 months after radiotherapy the patient suffered from serious dyspnoea and dysphonia. Laryngeal edema and an unknown mass in the anterior larynx commissure were seen during the ENT examination. During the direct endoscopy a “foreign body” was removed and edematous tissue was visualized in the surrounding region. Histological examination showed necrotical cartilage without evidence of cancer recurrence. After postoperative anti-edematous, mycolytic and antibiotic therapy the patient was discharged free of complaints.