The correlations between morningness-eveningness character (Horne & Ostberg score), sleep habits and temperature acrophase of 62 adolescents (mean age 13 years and 6 months) were investigated on three occasions at 6-month intervals. Horne & Ostberg scores ranged from 29 to 74 with a similar distribution on the three occasions. Temperature acrophase mode occurred around 15:00 p.m. Earlier sleep onset time and wake-up time and earlier temperature acrophase were associated with morningness. The more evening type the adolescent was, the shorter was the sleep length on schools days and the longer was the sleep length on non-school days. Correlations between temperature acrophase and morningness-eveningness character were found in a subgroup of adolescents and require further confirmation. The correlations between morningness-eveningness and sleep habits were present on the three occasions investigated, indicating that these are stable correlations and that morningness-eveningness questionnaires can provide suitable information for studies of this age group.