In 3 patients, two men aged 34 and 46 years and a woman aged 24 years, who appeared to have psychiatric disorders, neurosyphilis was diagnosed on the basis of screened blood tests. Treatment with intravenous benzylpenicillin alleviated the symptoms. In recent years the incidence of primary syphilis in the Netherlands has risen. There is a wide range of symptoms and the interpretation of serologic results is difficult, especially if there is co-infection with HIV; this disease also increases the chance of progression from primary syphilis to neurosyphilis. Patients admitted to clinical care are usually severely ill and are frequently uncooperative or present unclear histories. Detection at an early stage is vital, as adequate treatment prevents disease progression. This could be achieved by a general screening of clinical psychiatric patients for syphilis in addition to the screening of selected groups.