Peripheral ossifying fibroma (POF) is a lesion of the gingival tissues that predominantly affects women and is usually located in the maxilla anterior to the molars. The definitive diagnosis is established by histological examination, which reveals the presence of cellular connective tissue with focal calcifications. Surgery is the treatment of choice, though the recurrence rate can reach 20%. We present a clinical and histological review - including a detailed immunohistochemical analysis - of four cases of POF diagnosed and treated at our hospital. All four patients were women, and two were pregnant. The immunohistochemical study revealed that the proliferating cells showed myofibroblastic characteristics and did not express estrogen or progesterone receptors. The lesions showed clinically benign behavior. Our results indicate that POF should be considered as a myofibroblastic proliferation, and although the clinical characteristics suggest hormonal influence, we were unable to demonstrate the expression of hormone receptors in the proliferating cellular component.