INTRODUCTION: Benign pathologies of the nasopharynx are rare, and cysts may be congenital or acquired, depending on their location. When a drain is clogged, the cyst progresses with increasing secretions leading to symptoms, such as nasal obstruction, posterior rhinorrhea, and hearing loss. The treatment is surgical excision and marsupialization of the edges, reducing the possibility of relapse. OBJECTIVE: To describe a case of a Thornwaldt cyst as well as its etiology, diagnosis, and therapy as occurred at the Second Infirmary of the Department of Otorhinolaryngology at Santa Casa de Misericordia - RJ. CASE REPORT: A pardo man, 36 years of age, presented with neck pain and nasal obstruction, especially during the night, which started approximately 1 year prior. He brought his last cervical spine magnetic resonance image (MRI), which showed discrete and diffusive signs of spondyloarthrosis and a topographical cystic formation of the adenoid. Nasal endoscopy revealed a septal deviation to the right and a smooth mucosal mass located at the middle position of the nasopharynx, similar in coloration to the nasal mucosa. He underwent endoscopic nasal surgery with excision and marsupialization of the nasal mucosa. The histopathological examination confirmed nasal mucosal epithelium. The patient is being monitored in the infirmary without relapsing. CONCLUSION: Even though a Thornwaldt cyst is considered an uncommon disease, we would like to increase the awareness of its differential diagnosis from other benign diseases of the midline, such as mucous gland cysts, encephalocele, meningoencephalocele, chordoma, osteoma, and hemangioma, among others.