Patients with pheochromocytoma may be eligible for this study. Candidates will be screened with a medical history and physical examination, electrocardiogram, and blood and urine tests. Study participants will undergo blood, urine, and imaging tests, described below, to detect pheochromocytoma. If a tumor is found, the patient will be offered surgery. If surgery is not feasible (for example, if there are multiple tumors that cannot be removed), evaluations will continue in follow-up visits. If the tumor cannot be found, the patient will be offered medical treatment and efforts to detect the tumor will continue. Main diagnostic and research tests may include the following: