Nocturia frequently is considered a benign problem that results from aging. Nocturia can result from poorly controlled diabetes, congestive heart failure, or urinary dysfunction. Also a symptom of obstructive sleep apnea (OSA), nocturia is a significant source of sleep disruption that may result in excessive daytime sleepiness. This article examines variables that contribute to nocturia, its effect on health, and the physiological mechanisms in OSA that evoke nocturia. Evaluation requires differentiation of the underlying causes that result in either increased frequency or increased nocturnal urine production, including symptoms of OSA.