Study objectives. The temporal relationship between nocturnal sleep and daytime napping has only been assessed in small non-representative samples, and suggest that nocturnal sleep and napping are interdependent, although mixed results exist. We investigate the temporal relationship between nocturnal sleep and napping (and vice versa). Methods. A population-based sample of middle-aged adults (N=683, mean age 60.7 [SD 9.5]) completed seven days of ecological momentary assessment reporting sleep and nap characteristics. Multilevel random-effects models were used to assess the temporal relationship between sleep duration and quality and nap occurrence and duration (and vice versa). Results. 64% of the study population took at least one nap during seven days. Poor subjective sleep quality and shorter sleep duration increased the likelihood and duration of next-day napping. No effect of nap occurrence or duration was found on same-day nocturnal sleep duration and quality was found. However, when considering the timing of nap, afternoon naps, but neither morning nor evening naps, decreased same-day nocturnal sleep duration. Conclusion. Naps seem to compensate for poor subjective sleep quality, and to some extent for short sleep duration. As only afternoon naps reduced same-day nocturnal sleep duration, timing of the daytime nap seems to matter with respect to same-day nocturnal sleep duration.