The purpose of the study is to determine whether early initiation of ART  is superior with respect to neurocognitive function to deferring ART initiation until CD4+ counts decline to below 350 cells/mm3. The neurocognitive function is assessed by means of a neuropsychological quantitative performance test battery comprised of eight neuropsychological tests that assess neurocognitive functioning across a range of cognitive abilities; attention/speed of information processing, executive function, verbal learning/memory, language fluency, fine/ complex motor skills/speed and speed of information processing.

The goal of the Neurology substudy to enroll at least 600 participants was reached in May 2012. Participants will be followed to the common closing date of START.