The physical changes that accompany the onset of puberty demand a constant restructuring of the adolescent's perception of their body and may influence adolescents' mental health. To describe weight status perception and its association with socio-demographic characteristics (SDC) and mental health disorders among adolescents in a low and middle-income country (LMIC). We conducted a cross-sectional study in high schools in the urban area of the governorate of Sousse, Tunisia in 2018. We included in our study all students studying in selected classes in selected public high schools and who are consented to participate. Multinomial logistic regression was used to assess the associated factors to weight perception categories. The total number of students participating was 1399 with a response rate of 86.68%. The female sex was predominant (60.5% versus 39.5%). The mean age was of 17.03 ± 1.51 years. According to multivariate analysis, perceived weight categories were associated with sociodemographic factors such as gender and maternal educational level. Adolescents perceiving themselves as obese were at risk for severe depression (aOR = 0.40; p = 0.033). The BMI was associated with weight misperception: adolescents with normal weight tend to overestimate their weight (obesity aOR = 0.13, p = 0.017; overweight aOR = 0.1, p = 0.001). There was a clear discrepancy between the actual weight status of the teens and their self-perceived weight. Adolescents are still growing both physically and mentally, and forming their self-image. Thus, health promotion practices designed to create accurate perceptions of current body weight need to be part of prevention efforts.