The aim of this study is to offer preliminary results about the validity of the composite morningness scale (CS) and the early/late preferences scale (PS) in a Peruvian sample. The relationship of both scales with the preferred rising and retiring times was analysed, along with the level of self-reported alertness. In Bohle et al.'s (2001) work, the relationship between morningness and preferred rising and retiring times was higher over the weekend than on weekdays. This difference explained the dispositional nature of morningness, due to the possible lesser influence of time schedules over the weekend in individuals' preferences. This result is replicated in a group of 139 Peruvian undergraduates, aged between 18 and 29 years (M = 21.73), of whom 78.4% were women. The relationship between morningness and (actual) normal rising and retiring times on weekdays and over the weekend is considered. The results partially confirm Bohle et al.'s (2001) hypothesis about preferred rising and retiring times and their relationship with the PS, and actual rising time and its relationship with the CS and PS. The differences in the level of self-reported alertness between morning, intermediate and evening-oriented groups provide support for the validity of both scales. Finally, the scores of CS and PS in Peruvian undergraduates are similar to those found by Smith et al. (2002) in university students from six countries.