Purpose <p>Adult separation anxiety disorder (ASAD) is thought to be prevalent and debilitating, yet many aspects of its epidemiology remain unclear. We aimed to investigate prevalence, course, correlates, comorbidity, impairment, and treatment of ASAD in Saudi Arabia.</p> Methods <p>The study analyzed a subset of 1793 participants from the Saudi National Mental Health Survey; a nationally representative household sample of Saudi citizens. The survey used the CIDI 3.0 to produce prevalence estimates of ASAD and other common DSM-IV mental disorders. Cross tabulations, survival analysis and logistic regression were used to analyse the data.</p> Results <p>The lifetime and 12-month prevalence of ASAD were 7.6% and 3.8%, respectively. Over half (51.7%) of participants with lifetime ASAD had onset in adulthood, and 50.5% of those with lifetime ASAD also had 12-month ASAD. Lifetime ASAD was significantly associated with being female (OR = 2.1), not being married (ORs = 2.2–3.2), having low education (OR = 0.4), and maladaptive family functioning (ORs = 3.6–6.7). Primary lifetime ASAD was a strong predictor of subsequent other mental disorders (ORs = 1.1–6.5). Further, mood, impulse, and substance use disorders were significantly associated with subsequent first onset of ASAD (ORs = 2.15-3.0). ASAD was severely impairing in the presence (59.0%) or absence (56.2%) of 12-month comorbidity. Among those with lifetime ASAD, only 26.1% reported treatment for a mental health condition.</p> Conclusion <p>ASAD is prevalent, with a persistent course and associated impairment, as well as substantial comorbidity and limited treatment in Saudi Arabia. Increasing awareness, early diagnosis, and treatment of ASAD may help reduce its burden.</p>