Objectives: This study investigated if unhealthy sleeping habits of university students can be explained by the Theory of Planned Behavior. Method: An online questionnaire was administered to 1006 undergraduate students at a Belgian university to measure their frequency of irregular sleeping times, daytime napping, and pre-bedtime alcohol or internet use, as well as the attitudes, perceived norms, perceived control and intentions for these behaviors. Results: Principal Component Analysis and internal consistency analysis confirmed the validity and reliability of the scales measuring the TPB dimensions. Expected outcomes, perceived norms and perceived control significantly explained intentions to avoid irregular sleeping times, daytime naps, pre-bedtime activity and pre-bedtime alcohol use. Intentions and perceived behavioral control explained self-reported irregular sleeping times, daytime napping, pre-bedtime activity, and pre-bedtime alcohol use. Significant differences in predictions were found for gender, study program, type of residence and age. Conclusions: The TPB provides a useful theoretical framework to explain students' sleeping behaviors.