Objective: Despite the suspected link between carpal tunnel syndrome (CTS)—a common neuropathy—and psychiatric issues, long-term evidence, especially in Asia, remains scarce. This study investigated the long-term incidence of depression, anxiety, somatoform, and sleep disorders after CTS diagnosis in a South Korean nationwide cohort. Methods: Using the Korean National Health Insurance Service cohort (2002–2013), newly diagnosed CTS patients (2004–2013) were identified following a 2-year washout period. Each CTS patient was propensity score-matched 1:10 with non-CTS controls based on demographics and health status. Cox proportional hazards regression yielded adjusted hazard ratios (aHRs) for incident depressive, anxiety, somatoform, and sleep disorders over up to 10 years of follow-up. Results: Compared to controls, CTS patients had significantly elevated risks for all outcomes: depressive disorders (aHR, 1.59; 95% confidence interval [CI], 1.45–1.74), anxiety disorders (aHR, 1.41; 95% CI, 1.31–1.52), somatoform disorders (aHR, 1.38; 95% CI, 1.23–1.55), and sleep disorders (aHR, 1.36; 95% CI, 1.25–1.49). Risk was notably higher in individuals aged <60 years for all disorders. Males showed higher risks for depression, anxiety, and sleep disorders, while females had a slightly higher risk for somatoform disorders. Conclusion This comprehensive, longitudinal study indicated that CTS is associated with an increased long-term risk of psychiatric disorders. The findings emphasize comprehensive management strategies that integrate mental health screening and interventions tailored to age and sex among patients with CTS.