To analyze a series of carcinoma ex pleomorphic adenoma (CXPA) and to assess the diagnostic difficulties. The clinical presentation of 24 CXPAs was compared with 300 pleomorphic adenomas (PAs). Furthermore, pathohistological findings and follow-up results of CXPAs were evaluated. Eight of 24 (33%) CXPAs versus 41 of 300 (14%) PAs were localized in the deep lobe (P < 0.05). Forty-two percent of CXPAs versus 6 percent of PAs, respectively, were greater than 4 cm (P < 0.05). The sensitivity in detecting CXPA by fine-needle aspiration cytology (FNAC) was 47 percent. The tumor was known to be malignant preoperatively in 10 (42%) patients. Six of 24 (25%) patients with CXPA developed a tumor recurrence. The overall 5-year survival rate of CXPA was 76 percent. CXPAs are difficult to identify preoperatively. FNAC has a low accuracy and sensitivity. CXPAs versus PAs are significantly more frequently localized in the deep lobe and are significantly greater in size.