Background: Body image perception among adolescents is crucial for their mental health and is influenced by a variety of factors. Incorrect body weight estimation is common among this population and is usually overestimated by females and underestimated by males. Objective: This study aimed to evaluate body weight perception and related factors among adolescents aged 11 and 14. Material and Methods: This pilot study was based on data collected from the Polish health program “A program for the early detection of risk factors for lifestyle diseases SOPKARD-Junior” from the years 2015, 2017, 2019, 2021, and 2022. According to the BMI and weight perception, a total of 315 adolescents aged 11 and 14 were divided into three groups: “underestimating their weight”, “properly estimating their weight”, and “overestimating their weight”. These data were then compared to different psychosocial variables, such as parental education, life satisfaction, parental weight assessment, dieting, Family Affluence Scale (FAS), and subjective health. Results: Males underestimated their weight more often than females, while females overestimated their weight more frequently than males (all p < 0.001). These results were most prevalent for 14-year-olds. Dieting was observed in both age and sex groups, even despite being of normal weight. Moreover, dieting, parental weight assessment, and parental education were statistically significant factors related to children’s weight estimation. Discussion: Body weight misperception is prevalent among Polish teenagers aged 11 and 14. Factors, such as parental weight assessment or parental education, influence teenagers’ weight perception and should be investigated further. Conclusions: Incorrect weight perception is common among adolescents. Teachers, parents, and medical professionals, such as doctors or nurses, should be aware of this problem and provide proper education and support.