The aim of this study was to identify human immunodeficiency virus (HIV) protease mutations associated with virological response (VR) to fosamprenavir-ritonavir (FPV/r) in 113 protease inhibitor (PI)-experienced patients randomized in both CONTEXT and TRIAD clinical trials and receiving the same dose (700/100 mg twice daily) of FPV/r. The impact of each protease mutation on the VR to FPV/r, defined as the decrease in HIV RNA at week 12, was investigated with nonparametric analyses. A step-by-step procedure was done using a Jonckheere-Terpstra (JT) test that retains the group of mutations most strongly associated with the VR. Mutations at the following 14 codons were associated with a reduced VR to FPV/r: 10, 15, 33, 46, 54, 60, 62, 63, 72, 73, 82, 84, 89, and 90. The JT procedure led to selecting the CONTEXT/TRIAD genotypic set of mutations, I15V, M46I/L, I54L/M/V, D60E, L63P/T, and I84V, as providing the strongest association with the VR (P = 1.45 × 10−11). In the nine patients with zero mutations within this set, the median decrease in HIV RNA was −2.63 log copies/ml, and was −2.22 (n = 45), −1.50 (n = 26), −0.58 (n = 23), −0.47 (n = 6), −0.13 (n = 3), and 0.04 (n = 1) log copies/ml in those with one, two, three, four, five, and six mutations, respectively. This study identified six mutations associated with VR to FPV/r. Some of these mutations are shared with the current FPV/r Agence Nationale de Recherches sur le SIDA (ANRS) resistance score, which has been cross-validated in the CONTEXT/TRIAD data set, suggesting that the current ANRS FPV/r score is a useful tool for the prediction of VR to FPV/r in PI-experienced patients.