Mesothelioma is diagnosed through a comprehensive combination of biopsy and imaging scans.

Mesothelioma can be a difficult malignancy to diagnose because the symptoms of the disease closely resemble other respiratory conditions, and because the pathology can be very difficult to distinguish from adenocarcinoma of the lung. For these reasons, misdiagnosis is not uncommon in mesothelioma patients. Symptoms of mesothelioma include chest pain, chronic cough, effusions of the chest and abdomen, and the presence of blood in lung fluid.
Diagnostic surgeries, including a biopsy, will typically be required to determine the type of malignant cells that are present in the body. Typically a body imaging scan, including a magnetic resonance image (MRI), computer topography (CT scan), and/or positron emission tomography (PET), will be required to determine the extent and location of the disease. Given how rare mesothelioma is, a formal staging classification exists only for pleural mesothelioma