The primary objective is to establish the pharmacokinetic (PK) profile at steady state of nevirapine XR in HIV infected children from >=3 to <18 years of age. This phase I trial is an open-label, multiple dose, non-randomized and cross-over study. Patients who have completed the last visit of the PK trial (visit 7) can enter into an Optional Extension Phase (OEP) until the Investigational New Drug (IND) is withdrawn; until nevirapine XR becomes approved and is available by prescription in a given country; or, the patient enrolls in a compassionate use program. During this OEP, nevirapine XR safety and efficacy information will be collected.