Symptoms of mesothelioma take a long time to develop, which is a major reason for the high fatality rate. Symptoms include shortness of breath, difficult breathing, and pain in the chest or abdominal cavity. Chest pains indicate that the disease is aggravating the nerve cells in the tissues, and has reached a serious stage. Less severe chest discomfort and shortness of breath are generally due to the accumulation of fluid between the two layers of the pleura.

Mesothelioma of the abdomen can have symptoms of abdominal pain and swelling. Other symptoms include cough, fatigue and unexplained weight loss.

As chest pain, shortness of breath or abdominal pain are symptomatic of several diseases, tests are required to identify the cause. These tests vary depending on the symptoms and may include an electrocardiogram (EKG), and a chest or abdominal X-ray. If abnormalities are seen, a CT scan or an MRI scan is taken. These tests help determine the size, location and extent of a possible tumor.

Fine-needle aspiration may also be given. In this procedure, a thin needle is used to remove a small sample of the fluid in the abdomen or lungs for examination. A biopsy is also taken through a thoracoscopy or video-assisted thoracoscopy (VAT), or through a led laparoscopy. Here, a tube-like instrument inserted through a small incision gives a view of the tumor and collects a tissue sample. A bronchoscopy or a mediastinoscopy may also be done. This enables the doctor to look for other masses of tumors in the lungs or to take tissue samples from lymph nodes.