BACKGROUND: We conducted a nationwide registry-based study of the quality of diagnostic evaluation for dementia in the secondary health care sector. METHOD: Two hundred patients were randomly selected from the patient population (4,682 patients) registered for the first time with a dementia diagnosis in the nationwide hospital registries during the last 6 months of 2003. Through medical record review, we evaluated the completeness of the work-up on which the dementia diagnosis was based, using evidence-based dementia guidelines as reference standards. RESULTS: Satisfactory or acceptable completion of the basic dementia work-up was documented in 51.3% of the patients. Only 11.5% of those with unsatisfactory work-up were referred to follow-up investigations. Dementia syndrome was confirmed in 88.5% of the cases, but correct subtypes were diagnosed in only 35.1%. CONCLUSION: The adherence to clinical guidelines concerning dementia work-up is inadequate in the secondary health care sector. Our findings call for improvement in the organization of clinical dementia care, for education of specialists and for changes in attitude towards making a diagnosis of dementia.