Polyps of the maxillary sinus were obtained from six patients who had reported upper tooth extraction with oroantral perforation prior to the development of symptoms, from 11 patients with chronic sinusitis, and from 12 patients with allergy. Histopathological features, scanning electron microscopy of the polyp epithelium and clinical data were compared in those groups of patients. The post-traumatic polyps differed from those of other aetiologies by showing the presence of granulomas, less numerous inflammatory cells with very few eosinophils, nearly normal surface epithelium (smaller surface area occupied by nonciliated epithelium, absence of epithelial squamous cells, normal frequence of goblet cells), rapid appearance of symptoms, and shorter duration of the disease. It seems that the specific characteristics of the injury-induced polyps results from a different mechanism of their formation, involving primarily abnormal mucosal repair and to a lesser extent an inflammatory process.