(1) Background: Emotional regulation is a critical determinant of adaptive functioning during adolescence, exerting a profound influence on psychological well-being. This study seeks to deepen our understanding of the intricate interplay between emotional regulation and maladaptive psychological symptoms, examining these dynamics through a cross-country comparison. (2) Methods: A total of 224 adolescents, aged 13 to 21 years, from both Iran and Belgium, participated in a cross-sectional comparative study. The study aimed to elucidate the relationship between emotional regulation and mental health functioning, assessing internalizing symptoms, externalizing symptoms, and self-injury. A demographic questionnaire, the Emotion Regulation Inventory, the Strengths and Difficulties Questionnaire, and the Self-Harm Inventory, were administered. Data analysis incorporated correlation assessments, multivariate analysis of variance, and structured equation modeling. (3) Results: The findings revealed a positive association between emotional dysregulation and psychological symptoms across the entire sample. Conversely, emotional suppression, more prevalent in Iran, showed no significant link with maladaptive symptoms but was associated with self-harm in the Belgian sample. Cultural disparities were evident, with internalizing problems more prevalent in Iran and externalizing issues more common in Belgium. (4) Conclusions: Emotional dysregulation emerged as a common factor compromising mental health. It emphasizes the necessity of considering cultural nuances when developing interventional and preventative programs and calls for further research in this field.