The nighttime and daytime correlates of the insomnia complaint (IC) were assessed in an in-class survey on a sample of 1238 first year university students (18.85+/-1.45 years) at the Universidad Autónoma of Madrid, Spain. Evidence was found that the likelihood of complaining of insomnia was increased by perceiving difficulties with initiating and maintaining sleep, reporting low quality of nocturnal sleep, having a long sleep onset latency and having an evening circadian preference. The most strongly related daytime variables to IC being perceived difficulties in concentrating, feelings of irritability and fatigue, and symptoms of anxiety and depression. The data, in addition to confirm those of clinical studies on subjects complaining of insomnia, suggest that having an evening chronotype increases the vulnerability of adolescents and young adults to complain of insomnia.