Efavirenz (Sustiva®) is recommended as an option for use within NHS Wales in antiviral combination treatment for the treatment of human immunodeficiency virus-1 (HIV-1) infected children 3 months of age to 3 years and weighing at least 3.5kg. Sustiva® has not been adequately studied in patients with advanced HIV disease, namely patients with CD4 counts < 50 cells/mm3, or after failure of protease inhibitor (PI) containing regimens. Although cross-resistance of efavirenz with PIs has not been documented, there are at present insufficient data on the efficacy of subsequent use of PI based combination therapy after failure of regimens containing Sustiva®.