The most common bilateral tumor in the parotid gland is Warthin's tumor. Warthin's tumor is also the most common multisentric, or multifocal, tumor. Another name for Warthin's tumor is cystadenolymphomatosum. The parotid gland is the only major salivary gland that contains lymphoid tissue. Warthin's tumor develops from these lymphoid structures, and therefore, Warthin's tumor only arises from the parotid gland. It ranks second after pleomorphic adenoma among the most commonly encountered benign salivary gland tumors. Warthin's tumor is associated with smoking. Although it is not cancerous, it appears bright on PET scans. Warthin's tumor has no potential to transform into cancer, meaning it has no risk of malignant transformation.