Objective: To identify clinical, laboratory and demographic markers which are associated with the presence of dementia and neuropsychological impairment in severely immunodeficient patients. Method: Fifty-nine HIV+ patients participated in the study. Patients were assessed neurologically and neuropsychologically, and a subset of patients underwent lumbar punctures. Logistic regression was used to determine which variables from a set including age, education, IQ, depression, anxiety, CD4 cell counts, haemoglobin, serum and CSF â2 microglobulin and neopterin, constitutional symptoms, past opportunistic infections and use of antiretroviral therapy was associated with the occurrence of dementia and neuropsychological impairment. Results: An increased likelihood of neurological and neuropsychological dysfunction was associated with diarrhoea at some time in the recent past, elevated serum neopterin at the time of assessment, and increased age. A decreased likelihood of impairment was associated with a higher estimated IQ, more years of education, and the presence of an AIDS-defining illness at the time of assessment. Conclusion: Recent diarrhoea, elevated serum neopterin, advanced age and low education and IQ can serve as ''signals'' for the presence of neurological and neuropsychological dysfunction.