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Urinary cytology has a significant role in the detection and surveillance of patients with urothelial carcinoma (UC), which has a high morbidity rate in the United States. Examination of the urine is a comprehensive screen of both the upper and lower urinary tract and is ideal for detecting both primary bladder UC and synchronous or metachronous, multifocal UCs that commonly occur because of a “field effect.” This field effect is the result of both clonal and random genetic abnormalities that have resulted from exposure to carcinogens (most frequently in tobacco smoke) in conjunction with the individual's ability to repair DNA damage. Although urinary cytology has high specificity for the detection of UC, its sensitivity is relatively low, especially for more prevalent low-grade tumors. Consequently, several urine-based tests have been investigated, some of which are available commercially and approved by the US Food and Drug Administration. However, these tests also have their limitations and often have lower specificity than urinary cytology. Consequently, urinary cytology, which is a noninvasive, cost-effective test, continues in mainstream use because of its ability to detect high-grade, flat lesions that can be difficult to detect clinically and that often have more aggressive biologic behavior.