Over the past 20 years, the ultrasound study of the urinary bladder has been improved by technology. It is reliable, low cost, and easy to perform also in an outpatient setting using a portable device. This is an irreplaceable tool for the urologist in the diagnosis and follow-up of benign and malignant diseases of the lower urinary tract. However, ultrasound quality is operator dependent. Therefore, it is crucial to establish limits and diagnostic accuracy. We summarized recommendations to obtain an appropriate ultrasound examination and understanding of the bladder morphology, which varies according to the different phases of bladder filling.