Objectives: To measure cerebrospinal fluid (CSF) ferritin in HIV infected patients with acute neurological episodes and to correlate the findings with the type and severity of neurological disease. Methods: CSF ferritin and the ratio of CSF to serum albumin (QAlb) were prospectively measured in 27 consecutive HIV infected patients admitted to a specialist unit for investigation of acute neurological episodes; the results were compared with their clinical diagnoses. Results: Ten patients had HIV associated dementia complex, six had cryptococcal meningitis, two had primary CNS lymphoma and nine had miscellaneous conditions including herpes simplex virus encephalitis, cytomegalovirus encephalitis, cerebral toxoplasmosis and mononeuritis multiplex. Overall, 16 (59%) patients had raised CSF ferritin levels, ranging from 13.0 to 50.2 μg/l, (median = 16.1 μg/l: normal range 1.0-12.0 μg/l). Thirteen of the 16 also had normal QAlb values, implying an intact CSF-blood barrier, and thus that local synthesis of ferritin had occurred. Elevated ferritin levels were not associated with particular neurological diagnoses. In those with HIV associated dementia complex there was no correlation between CSF ferritin levels and the severity of clinical cognitive deficit or the extent of magnetic resonance imaging abnormalities. Conclusions: An elevated CSF ferritin level is a non-specific finding in HIV infected patients presenting with acute neurological episodes.