peer reviewed ; PURPOSE: GADIS aims at determining the prevalence of generalized anxiety disorder (GAD) and major depression (MD) in primary care and their impact on the patient's functioning in Belgium and Luxemburg. METHOD: A large scale screening program was conducted at the consultation of general practitioners to detect patients with GAD and MD according to DSM-IV criteria. We collected additional data regarding the use of hypnotic, tranquilizer, antidepressant and analgesic medications. Impact on the patient was assessed with the Sheehan disability scale. RESULTS: Three hundred GP's in Belgium and Luxemburg were asked to screen 50 consecutive patients. Of the 13,677 analyzed patients, 8.3% were diagnosed to have GAD and 6.3% MD. Comorbidity was observed in 4.2% of patients. The prevalence was much higher in the French-speaking part of Belgium. GAD and MD were associated with impairment in social, familial and professional functioning. Only a minority of patients with GAD and/or MD was treated with an antidepressant and almost half of subjects with GAD and/or MD were treated with a tranquilizer. CONCLUSION: Prevalence rates of GAD and MD in primary care in Belgium are comparable to other countries. GAD and MD are disabling conditions. Antidepressants are still used only in a minority of subjects with GAD and/or MD in primary care in Belgium and Luxemburg. The prevalence of GAD and MD appears to be much higher in French-speaking parts of Belgium.