There are three basic types of malignant mesothelioma, with a variety of symptoms and diagnostic criteria. The basic types depend on which part of the mesothelium develops the cancer. Peritoneal mesothelioma develops in the lining of the abdominal cavity, around the stomach and intestines. Pericardial mesothelioma develops in the pericardium, the chamber that surrounds the heart. Pleural mesothelioma, the most common variety, develops in the pleura, the lining of the thoracic cavity which contains the lungs.

Pleural mesothelioma is difficult to diagnose because the symptoms present nearly identically to those of viral pneumonia. Diagnosis is made even more difficult because patients often have secondary infections like pneumonia or bronchitis; simply treating the obvious symptoms the patient has can add weeks or months to the time required to make a correct diagnosis. The symptoms of pleural mesothelioma include shortness of breath, chronic cough, and chest pain. Chest x-rays often show the presence of liquid in the lung cavity, called pleural effusion.

Pleural mesothelioma is the most common form of the disease, largely because the most direct route of asbestos exposure is to breathe asbestos fibers into the lung, where they burrow into the soft tissue and begin causing damage immediately.

Peritoneal mesothelioma comes in two different varieties. One form, in which the mesothelioma tumor is encysted by the body, used to be considered a benign form of the disease, but it has become apparent that this form is not benign as it usually serves as a precursor to the non-cystic form. The symptoms of peritoneal mesothelioma are pain and swelling of the abdomen, weight loss, nausea, bowel obstruction, anemia, swelling of the feet, and frequent urination. Many patients also develop a palpable abdominal mass.

Pericardial mesothelioma is quite rare and has not been studied with the intensity of the other two forms of this malignant cancer. Pericardial mesothelioma causes production of excess fluid in the pericardium, which can generate heart palpitations as the tumor and the liquid put pressure on the heart muscle. The fluid flow, called a pericardial effusion, makes it more difficult for blood to flow into the heart and makes the heart pump less efficiently. Many of those suffering from pericardial mesothelioma have symptoms they interpret as a heart attack, since there is pain in the heart area. Pericardial mesothelioma sufferers often have liver pain and congestion, which is a key sign that a pericardial cancer should be investigated.

Another extremely rare form of malignant mesothelioma is mesothelioma of the tunica vaginalis, a membrane surrounding the genitals. This generally begins with a small tumor forming on a testicle, and the formation of a hydrocele, which is a fluid-filled sac that forms around the testes. This is an extremely rare form of malignant mesothelioma, however.