In the Ohio River basin, the northern madtom, Noturus stigmosus Taylor, is morphologically similar to and sympatric with the mountain madtom, Noturus eleutherus Jordan. Although recognized as distinct sympatric (and syntopic) species, N. stigmosus and N. eleutherus are difficult to distinguish in streams where they are associated, based on previously defined characters. Sheared principal component analysis (PCA) of morphometric data revealed characters that more effectively differentiate the two species. Noturus stigmosus differs from N. eleutherus in having longer pectoral fins and spines, a longer dorsal fin and spine, a shorter and higher adipose fin, and a longer first dorsal saddle. As juveniles (20–30 mm standard length), N. eleutherus more closely resembles N. stigmosus on the basis of morphometry and pigmentation, but differs from the former in lacking a distinct dark adipose blotch. Meristic comparisons indicate that the two species differ most consistently at sizes > 30 mm SL in the numbers of caudal fin rays (usually > 48 in N. stigmosus vs. < 47 in N. eleutherus) and preoperculomandibular (POM) pores (modally 11 in N. stigmosus vs. 10 in N. eleutherus).