Introduction. Peritoneal mesothelioma is a rare tumor, presenting difficulties in diagnosis and treatment. Peritoneum is the second most common area of the mesothelioma after pleura, and even synchronous pleural and peritoneal mesotheliomas are observed in 30–45% of all cases. The diagnosis may be difficult due to lack of specific symptoms and clinical findings. In addition, a delay in the diagnosis is not rare especially in the absence of previous asbestos exposure. Here we report two cases of malignant peritoneal mesotheliomas. The diagnostic and therapeutic approaches for these rare neoplasms are discussed. Case Presentation. The cases were two men (one aged 54 years old and the other 40 years old). Prolonged abdominal pain and swelling were the primary presentation symptoms and findings. The mesotheliomas were developed in the right upper quadrant of abdomen in both of the cases. Both cases were treated with surgical resection. Final diagnosis were possible with histological and immunohistochemical documentation of tumor characteristics, which were consistent with dictating a mesothelial origin. No history of asbestos exposure was reported. Conclusion. Peritoneal mesotheliomas are rare clinical entities. However, patients with prolonged abdominal pain and abdominal masses should be considered to have atypical pathologies such as peritoneal mesotheliomas.