Introduction: Routine neonatal screening for congenital hypothyroidism (CH) has improved the prognosis for screened patients since its widespread implementation in France in 1979. Objectives: The objective of this study was to assess the health status and sociodemographic characteristics of young adults treated for CH since the neonatal period. Methods: All patients (n=1,748) screened during the first decade following the introduction of neonatal screening in France were selected for the study. They were invited to complete a standardized questionnaire; 70% (n=1,202) of the initial cohort responded; their median age was 23.4 years. The results were compared to a reference population (n=5,817) from the 2003 Decennial Health Survey. Results: The majority of patients reported satisfactory health status and social integration. However, compared to the reference population, the patients reported a higher proportion of associated chronic diseases (5.7% vs. 2.9%), hearing loss (9.5% vs. 2.5%), visual problems (55.4% vs. 47.9%), as well as higher rates of overweight and obesity (22.8% vs. 15.7%). The proportion of patients in the highest socioeconomic class and with full-time employment was slightly lower, at 14.6% vs. 23.1% and 39.9% vs. 44.8%, respectively (p<0.0001). A greater number of them still lived with their parents and had a slightly lower quality of life in terms of the mental component. Factors affecting educational attainment and quality of life included the initial severity of the condition, the persistence of hypothyroidism into adulthood—most often linked to poor treatment adherence—the presence of a chronic comorbid condition, and the presence of hearing loss and obesity. Conclusion: Optimal treatment and management starting in the neonatal period, early identification of any comorbidities, and educational strategies to improve long-term treatment adherence—particularly during adolescence and the transition to adult care—should improve the long-term prognosis.