Sleep disturbances, particularly insomnia, are common in school settings for adolescents. They affect the physical and mental balance with multiple consequences: various pain, fatigue, errors, reduced academic performance, drowsiness in class, repeated absences etc. We conducted a cross-sectional study using a questionnaire and the Epworth sleepiness scale with students from schools in the department of Thiès. The prevalence of insomnia was 21%, with a female prevalence. The average duration of sleep was 8.72 ± 1.1 hours with a variation according to the holidays, the days with or without class the next day. Risk factors are found, in particular living with a tutor other than the parents, the distance of the school from his place of residence, and the morning lesson schedules. Insomnia is significantly associated with sleep debt and excessive daytime sleepiness.