Book excerpt: Exfoliative and instrumented (catheterized) urines are the most common types of specimens evaluated in a cytology laboratory. The typical clinical presentation is a patient with new onset of urinary symptoms, asymptomatic hematuria, or patient with prior history of urothelial carcinoma on routine surveillance. A careful examination of exfoliated cells from the urinary tract can lead to a fast, relatively simple, economical and accurate cytopathologic diagnosis, which is crucial for timely patient management. However, there are a number of common non-neoplastic reactive conditions that can morp.