Diagnosis of mesothelioma includes history, physical exam, and histologic findings. Clinicians should have a high index of suspicion in any patient with a history of asbestos exposure 30 to 40 years prior to presentation. Exposure can occur in asbestos workers, family members of asbestos workers, and those living close to naturally occurring asbestos soil deposits. Common signs and symptoms at presentation include dyspnea, pleuritic or non-pleuritic chest pain, fatigue, weight loss, and pleural effusion. Asymptomatic patients may have pleural effusions that are found incidentally on physical exam or through radiographic studies. Thoracentesis decreases pleural effusions in 90 percent of patients, but cytologic studies of the pleural fluid are typically non-diagnostic. In suspected cases, thorascopically guided biopsy should be performed and is 98 percent diagnostic. A variety of immunohistochemistry stains should be performed to aid in diagnosis and to help distinguish mesothelioma from other lung neoplasms.