Background: There are limited data on the pharmacogenetics and pharmacokinetics of the CNS penetration of efavirenz. Objectives: We investigated genetic polymorphisms associated with CSF concentrations of efavirenz and its metabolites and explored the relationships with neurocognitive performance. Methods: We included 47 HIV-infected South African black adults with and without HIV-associated neurocognitive disorder on efavirenz/tenofovir/emtricitabine and collected paired plasma-CSF samples. We considered 2049 SNPs, including SNPs known to affect plasma efavirenz exposure, from potentially relevant genes (ABCC5, ABCG2, ABCB1, SLCO2B1, SCLO1A2, ABCC4, CYP2B6 and CYP2A6) and 880 met a linkage disequilibrium (LD)-pruning threshold. Results: We identified 9 slow, 21 intermediate and 17 extensive metabolizers. The CYP2B6 983 genotype in multivariate analyses predicted log 10-transformed concentrations of plasma efavirenz (b " 0.38, P " 2.7%10 #03), plasma 7hydroxy-efavirenz (b " 0.59, P " 3.7%10 #03), plasma 8-hydroxy-efavirenz:efavirenz ratio (b " #0.31, P " 1.8%10 #04) and CSF efavirenz (b " 0.36, P " 0.01). Lower plasma 7-hydroxy-efavirenz concentrations were independently associated with CYP2A6 rs10853742 (b " #0.55, P " 3.5%10 #05), ABCB1 rs115780656 (b " #0.65, P " 4.1%10 #05) and CYP2A6 #48A!C (b " #0.59, P " 0.01). CYP2A6 #48A!C was independently associated with higher CSF 8-hydroxyefavirenz:efavirenz ratio (b " 0.54, P " 0.048). CYP2B6 rs2279345 polymorphism was associated with lower plasma 7-hydroxy-efavirenz:efavirenz ratio in multivariate analyses (P , 0.05). No polymorphisms were associated with CSF:plasma ratios of efavirenz, plasma or CSF concentrations of 8-hydroxy-efavirenz or neurocognitive performance. Conclusions: We identified novel genetic associations with plasma efavirenz, plasma 7-hydroxy-efavirenz, plasma 7-hydroxy-efavirenz:efavirenz ratio, plasma 8-hydroxy-efavirenz:efavirenz ratio, CSF efavirenz and CSF 8-hydroxy-efavirenz:efavirenz ratio.