Purpose <p>Social disconnection has been linked to adverse health outcomes, including higher risks of mental disorders. However, previous studies have primarily focused on depression, with limited exploration of other mental disorders and demographic variations. This study investigates the association between social disconnection and a range of subsequent mental disorders in a large, population-based cohort.</p> Methods <p>A cohort study was conducted using data from 162,483 participants of the Danish National Health Survey, linked to national health registers. Social disconnection was assessed through survey measures of loneliness, social isolation, and low social support. Incident cases of mental disorders were identified using hospital-based diagnoses and included in seven categories. Poisson regression was applied to estimate incidence rate ratios (IRRs) adjusted for demographics, country of birth, and socio-economic resources.</p> Results <p>Individuals who were socially disconnected had a higher incidence rate of mental disorders in all seven categories: substance use disorders, schizophrenia spectrum disorders, bipolar disorder, major depressive disorder, neurotic and anxiety-related disorders, personality disorders, and a combined category of any aforementioned disorder. Loneliness overall showed the strongest associations (range of IRRs, 2.94 to 4.94) compared to social isolation (range of IRRs, 1.47 to 4.80) and low social support (range of IRRs, 1.32 to 2.82). While associations were generally similar across sexes, contrasting age trends were indicated for loneliness and social isolation.</p> Conclusion <p>Strong associations were consistently found between social disconnection and subsequent mental disorders, highlighting the potential for targeted public health interventions. Future research should investigate causal mechanisms and directional relations to refine prevention strategies.</p>