Apical periodontitis is an inflammatory pathology that affects the periapical tissues of a devitalized tooth. The aim of this study was to histologically and morphometrically characterize lesions of cysts and granulomas using light microscopy. Six biopsies obtained from teeth with indication of exodontia were analyzed. The histological analysis was carried out by means of optical microscopy and microphotographs, with contrast analysis of images and cell count by ImageJ. A description of the histological characteristics was made, observing the cavities surrounded by stratified squamous non-keratinized epithelium and a fibrous capsule composed of fibrocytes, fibroblasts and chronic inflammatory infiltrate; in the granulomas, capillaries, a fibrous capsule of fibrocytes/fibroblasts and a predominantly lymphocytic inflammatory infiltrate were observed. In relation to quantification of the cellular number of inflammatory infiltrate, for cysts it was of 9.2 cel / 10000 mm2, while for granulomas it was 20.8 cel / 10000 mm2, without significant statistical differences between both (p = 0.654). The quantification of the fibrocyte / fibroblast cell number was, for cysts, 15.4 cells / 10000 mm2, while for granulomas it was 18.5 cells / 10000 mm2, without significant statistical difference (p = 0.499). With respect to the percentage of collagen type I, for the cysts was 37.8 ± 19.2%, while for granulomas it was 33.8 ± 23.3%, without significant statistical differences (p = 0.704). A moderate negative correlation was observed for the inflammatory infiltrate (R = 0.667) and a low positive correlation for fibrocytes / fibroblasts (R = 0.121), in relation to the amount of type I collagen. Measurement of the area of the periapical lesions: the total average of lesions were 10.7 ± 5.0 mm2, the largest being a cyst of 18.1 mm2 and the smallest a granuloma of 5.2 mm2. The histological analysis allows to make a differential diagnosis of lesions with similar characteristics and thus define the most appropriate treatment.