Psilorhynchus robustus is most similar to P. gracilis and P. balitora in overall body shape, meristics and colour pattern. It is distinguished from both species by the presence of a large dark blotch situated posterodorsally to opercle opening, extending along lateral-line scales 3–6 (vs. absence) and in having upper lip separated from the rostral cap by a shallow groove (vs. upper lip separated from rostral cap by a deep groove).