Includes bibliographical references (leaves 33-42). / Aim: Neurological involvement related to HIV-1 infection is well described in the paediatric population and causes significant morbidity and mortality. This study aimed to describe specific neurological and neurobehavioural complications in this population. Method: Children infected with HIV-1 attending infectious diseases clinics were recruited for general and neurological assessments, developmental history screening and categorization of behavioural phenotype using the Aberrant Behaviour Checklist (ABC). Results: Eighty patients were assessed (males - 44/80: females - 36/80) (median age 5 years 1 month; range: 3 months - 12 yrs). Eighteen patients (23%) were not on antiretroviral (ARV) therapy at the time of testing. The Centre for Disease Control (CDC) immune categories of the patients at the time of assessment were: Category 1- n=6/80, Category 2- n=15/80 and Category 3- n=59/80. Thirty-three percent had a history of chronic lung disease, 10% had a history of an opportunistic central nervous system infection and 12.5% had epilepsy. 5 5 Anthropometric measurements identified that 19% of the patients were microcephalic, 17% of the patients were < 60% of their expected weight, 49% were 60-80% of expected weight and 45% were stunted. On neurological assessment 41% of the patients had global pyramidal tract signs, 7% had a hemiparesis, 5% had peripheral neuropathy, 16% had visual impairment, and 6% were hearing impaired. Of those who were screened for developmental deficits (patients < 6years of age) 66% had gross motor delay, 75% had fine motor delay, 70% had language delay and 73% had cognitive delay. Forty one percent had HIV Encephalopathy, 81% of whom a CD4 count < 15% and 48% were < 1year old. On the aberrant behaviour checklist (ABC) scale 24/80 patients had features of hyperactivity and 22/80 patients scored in the mild-moderate range on the lethargy / social withdrawal sub-scale reflecting a correlation with the affective and adjustment disorders. Conclusion: Diverse neurological and neurobehavioural deficits are common in children with HIV-1 infection especially those with CD4 < 15%, not on ARVs, with growth impairment and < 1yr of age. This study demonstrated the extent and spectrum of neurobehavioural and neurological complications in a defined HIV population. It stresses the need for early initiation of ARVs in the planning for future regimens and guidelines.