BACKGROUND To compare steady-state (ss) pharmacokinetic targets of nevirapine extended-release (NVP-XR) tablets once-daily (QD) with immediate-release (NVP-IR) tablet or oral suspension twice-daily in HIV-1-infected children and adolescents. METHODS Phase I, open-label, multidose, cross-over study with optional extension phase, in 85 patients 3 to <18 years of age, previously on an NVP-IR-based regimen for ≥18 weeks with baseline viral load <50 copies/mL. Patients were stratified by age, treated with NVP-IR twice-daily for 11 days, then NVP-XR QD for 10 days. Cpre,ss (steady-state, predose concentrations) was obtained from all, and 12-hour NVP-IR and 24-hour NVP-XR steady-state pharmacokinetic profiles were obtained in the pharmacokinetic substudy. Viral loads, CD4 counts and adverse events (AEs) were monitored. RESULTS Eighty patients completed the trial. Adjusted geometric mean (gMean) Cpre,ss for NVP-XR and NVP-IR exceeded the target of 3000 ng/mL, and the adjusted gMean NVP-XR:NVP-IR ratio (90% confidence interval) for QD normalized and un-normalized Cpre,ss were 91.2% (83.5-99.6%) and 91.8% (83.7-100.7%). gMean 24-hour area under the curve at steady-state NVP-XR:NVP-IR for un-normalized dose was 90.4% and un-normalized Cpre,ss NVP-XR:NVP-IR were 91.0%, 81.9% and 103.7% for the 3 age groups, 3 to <6, 6 to <12 and 12 to <18 years, respectively. gMean values indicated no exposure to subtherapeutic NVP concentrations and viral suppression was adequate and maintained in all QD groups. Most AEs were mild and similar between age groups. No serious or Division of AIDS Grade 4 AEs or AE related treatment discontinuations occurred. CONCLUSIONS NVP-XR exhibited adequate trough concentrations with equivalent area under the curve at steady-state relative to NVP-IR. NVP-XR was well-tolerated and is a valuable treatment option for HIV-infected children and adolescents.