The species of the Oriental and Papuasian genus Cryptoxyleborus Schedl in the Scolytine tribe Xyleborini are reviewed. Two new species, C. cuneatus and C. mawdsleyi are described from Brunei Darussalam. The following new synonymy is proposed: Cryptoxyleborus oxyurus Schedl ( = Cryptoxyleborus shoreae Browne syn.n.), Cryptoxyleborus vestigator (Schedl) ( = Platypus goilalae Schedl syn.n.). The following new combinations are given: Cryptoxyleborus acutus (Schedl) comb.n., Cryptoxyleborus percuneolus (Schedl) comb.n., both from Xyleborus; Microperus nanus (Browne) comb.n. from Cryptoxyleborus. A lectotype is designated for C. percuneolus, and the previously unknown male is described. A key is given to 18 species currently included in the genus, and new distributional records for many species. All species of Cryptoxyleborus are ambrosia beetles associated with dead or dying trees of the family Dipterocarpaceae, but are not of significant economic importance.