Brevibora exilis differs from B. cheeya and B. dorsiocellata by having the following diagnostic characters: 10 scales around caudal peduncle (vs. 12); anterior outline of the dorsal-fin blotch ranging from 2nd branched ray to first four or five branched rays with transparent inter-radial membrane between 1st and 2nd unbranched rays (vs. blotch reaching from 1st unbranched ray and inter-radial membrane between 1st and 2nd unbranched rays not hyaline); and shallow body depth (19.3-24.7% SL vs. 24.4-26.7 in B. cheeya; 25.8-28.4 in B. dorsiocellata). It can be further diagnosed from B. cheeya by having incomplete lateral line with 6-10 perforated scales (vs. 25-30), shorter head length (23.7-26.7% SL vs. 28.5-30.0), shallower caudal peduncle depth (10.4-11.9% SL vs. 11.7-13.0), shorter prepectoral length (25.9-27.3% SL vs. 29.6-29.3) and shorter dorsal fin length (22.0-24.6 % SL vs. 26.2-29.3). It can be further separated from B. dorsiocellata by the possession of 28-31 scales along the lateral line row (vs. 25-27) (Ref. 95539).