<p>Carcinoma ex pleomorphic adenoma (CXPA) has been considered an interesting model of carcinogenesis, presenting various histological subtypes and invasiveness phase. The objective was to determine the proliferative index of CXPA and comparing to pleomorphic adenoma (PA). Thirty six cases of CXPA (36 PA) and 22 areas of PA in CXPA (residual PA) were studied by Ki-67 expression. All CXPA cases were classified according to invasiveness phase (intracapsular, minimally and frankly invasive) and histopathological subtypes. Data was statistically analyzed by Wilcoxon, Mann-Whitney and Kruskal-Wallis tests. CXPA included 5 intracapsular, 9 minimally invasive and 22 frankly invasive cases. Fifteen cases corresponded to salivary duct carcinoma, 7 to adenocarcinoma NOS, 7 myoepithelial, 5 epithelial-myoepithelial, one case of squamous cell and one case of sarcomatoid carcinoma. The Ki-67 index of PA and residual PA were significantly lower than CXPA. Intracapsular and minimally invasive showed smaller proliferative index than frankly invasive. Considering the subtypes of CXPA, there was not a statistic difference among them. Ki-67 is a useful marker in the differential diagnosis of PA and CXPA, even when in the early invasive phase.</p>