Insomnia complaints increase with age and are frequently made by elderly people. Recently non-pharmacological treatments have been proposed more often, among which stimulus control. One of the stimulus control instructions is the advice not to nap in the daytime, based on the assumption that napping affects sleep quality the following night, due to a decrease of sleep need. This article discusses the function of napping and the impact of napping on sleep. The decline of sleep duration during aging is not due to a disturbance of the endogenous circadian rhythm but rather to a decrease of the physiological sleep need. Naps do not have the function to compensate for the decreased sleep duration but to meet an increased psychological sleep need. During daytime elderly people are physiologically less sleepy than young adults, who, nevertheless, sleep on average longer. Napping does not negatively affect sleep. Consequently, the assumption on which the advice against napping is based is wrong.