Morphological variation among Turkish populations of the Atlantic horse mackerel Trachurus trachurus (Carangidae) was examined for 150 specimens at five different sampling localities (Sea of Marmara (Istanbul and Canakkale), Aegean (Izmir) and Northeastern mediterranean (Antalya and Iskenderun) seas) in Turkey by discriminant function analysis of eleven morphometric and five meristic characters. The results of discriminant function analysis showed that there is limited gene flow among T trachurus populations in Turkish coastal waters. The Marmara Sea sample was similar to the Aegean Sea samples for both morphometric and meristic data. Morphometric and meristic data showed the heterogeneity between Aegean and Mediterranean mackerel samples. The Mediterranean samples separated from all others and indicate 2 local populations (Iskenderun and Antalya) for morphometric data, unlike meristic data that revealed no significant differentiation between 2 Mediterranean localities. Discriminant function analyses indicated that morphometric differentiation between the samples was largely due to differences in the head characters of fish. It is confirmed that metric characters are much less effective for discriminating between T trachurus populations than morphometric characters, which is expressed higher distances between samples. The results indicate a small degree of spatial separation in morphology in T. trachurus among the studied localities.