A 35-year old man was presented with organic psychosyndrome. Anamnestic reports informed about changes in his behaviour like loss of interest, reduced concentration and short-term-memory loss within the last 2 years. The practicing psychiatrist diagnosed a depressive syndrome in conjunction with a borderline syndrome and administered antidepressive and neuroleptic therapy. Specific serologic tests were not done. Neurologically, there was a picture of influent and slurred speech, and ataxic gait. Muscle tonus was normal, muscle reflexes were of the same diminished intensity on both sides. The psychic status revealed a person mostly oriented in time, location and situation but with severe disorders of recognition, concentration, and memory. Laboratory diagnosis proved the suspected diagnosis of neurosyphilis. Additionally, there were antibodies to Borrelia burgdorferi (Bb) in serum and CSF and a positive CSF/serum index of 9.0 (threshold: 1.9). The neuroradiologic examination (CCT, NMR, SPECT) showed an intense, diffuse, frontotemporal atrophy of the cortex. By NMR, massive gliosis was found in both hippocampi. Angiographically, an aneurysma (1 cm in diameter) of the medial cerebral artery was demonstrated. Specific treatment was performed with Na penicillin (5 Mio. i.v./4 h over 21 days). No remission could be achieved.