Trichomycterus hualco, new species, is described from an Andean stream in the Provincia de La Rioja, Argentina. The new species is distinguished from other species of Trichomycterus in the combination of the number of odontodes on the opercle and interopercle, the degree of exposure of the odontodes on the interopercle, the form of the premaxillary teeth, the presence of papillae-like structures on the body, the number of vertebrae, the position of the first proximal dorsal-fin pterygiophore, the form of the supraorbital canal within the frontal, the length of the lateral-line canal, and various meristic features.