Detailed morphological analysis of 76 specimens of Salmo marmoratus from rivers draining to the Adriatic Sea and 295 specimens of other Salmo species shows that it is possible to diagnose S. marmoratus from remaining Salmo species, including a marbled S. trutta from the River Otra in Norway, using colour pattern alone. S. trutta from the River Otra have pronounced white leading edges followed by black on anal and dorsal fins irrespective of the extensive variation in colour pattern on head and trunk. This pigmentation on the fins, commonly found in Atlantic basin S. trutta, is missing in S. marmoratus. Except for the marbled colour pattern in some specimens, S. trutta from the River Otra resemble Atlantic basin S. trutta in morphology. In multivariate statistics the combination of a high number of vertebrae, high proportion of abdominal vs. caudal vertebrae, and few caudal fin procurrent rays, separates S. marmoratus from remaining Salmo species. The recognition of S. marmoratus as a distinct species is also supported by published osteological and molecular data. Morphometry is less informative but S. marmoratus is characterised by a less deep but wider body compared to other Salmo species. However, the variation and overlap with other Salmo species is extensive. Salmo carpio and S. letnica inhabiting Adriatic drainages, are closer to S. salar than to S. marmoratus or S. trutta in morphometry. Thus, the two-species view, prevailing among fishery biologists and geneticists, only recognising S. salar and a polymorphic brown trout, S. trutta in Salmo is not supported by morphological data and disregards distinct, diagnosable, evolutionary units.