Voiding diary is the quantitative documentation of the timed amount of fluid intake and volume of urine passed for a 48-hour period. It includes unusual events such as leakage and straining besides frequency. It reflects natural voiding behaviour of the bladder in a natural setting, hence less prone to artefacts. In a small non-toilet-trained baby, a 4-hour voiding observation is the nearest equivalent. Being non-invasive, these diaries are easily available tools for follow-up assessments. This chapter deals with the practical aspects of maintaining a voiding diary and interpreting it.