Antrochoanal polyps (ACP) are benign lesions that arise from the mucosa of the maxillary sinus, grow into the maxillary sinus and reach the choana, and nasal obstruction being their main symptom. It is an interesting model to compare the pathophysiological mechanisms with those of bilateral nasal polyposis (NP). There is a lack of research in some areas of ACP, which have to become the main aims for future investigations of this disease. In comparison to NP, ACPs are usually unilateral and appear in younger patients. Macroscopically, they have a cystic intramaxillary portion and a solid intranasal portion. Microscopically, they are similar to a maxillary cyst of the mucosa. Nasal endoscopy, computed tomography and magnetic resonance are the main diagnostic techniques. Surgery is the indicated treatment for ACP, with endoscopic resection the most recommended. Simple avulsion of the polyp has a high rate of recurrence, whereas the Caldwell-Luc procedure is associated with damage of the maxillary and dental growth centres. More research is needed to establish the relationship between chronic sinusitis and ACP. Further work is also needed to investigate the role of inflammatory mediators (histamine, IgE, adhesion molecules, PAF), as well as metalloproteases and nasal remodelling, and tumour marker expression in A CP.