The feeding migration to the sea and the associated faster growth is an essential part of the ecology and life history of Atlantic salmon (Salmo salar L.). Thus the quantification of growth is an important part of fisheries research. The most productive feeding areas have a key role in the conservation of wild stocks and at the same time ensuring sustainable exploitation of reared stocks. The aims of this study were to investigate if there are spatial, temporal and stock (wild, reared) related differences in the growth of salmon in the Baltic Sea and to determine if individual diet preferences, prey species stock abundance and water temperature affect growth. The absolute length growth of Baltic salmon first and second sea growth season was back-calculated from time series (1989–2010) of archived salmon scales obtained from the main salmon feeding areas (ICES subdivisions (SDs) 25, 26, 28, 30 and 32). During first sea growth season wild salmon caught from SD25 (Main Basin) were fastest growing and individuals caught from SD30 (Bothnian Sea) grew slowest. Reared salmon caught from SD32 (Gulf of Finland) grew fastest during first sea growth season and individuals caught from SD26 (Main Basin) the slowest. During second sea growth season wild salmon caught from SD28 (Main Basin) were fastest growing and individuals caught from SD30 grew slowest. Reared salmon caught from SD25 had the fastest growth during second sea growth season and individuals caught from SD30 the slowest. There was a general increasing trend in the growth of wild salmon, recent growth during first sea growth season being annually 25 cm and during second sea growth season 30 cm. At the beginning of the study period reared salmon growth during first sea growth season was 20 cm, but since 1994 it has stayed close to 25 cm. Their growth during second sea growth season has been increasing through-out the study period from <15 cm close to 30 cm. Wild salmon grew faster than their reared counterparts during both sea growth seasons. Higher trophic position of salmon was associated with increased growth during second sea growth season in the Main Basin. Since trophic position reflects dietary behaviour, this indicates that diet has an influence on growth. Warmer water was associated with decreased growth during first sea growth season in the Gulf of Finland and during second sea growth season in the Main Basin. Salmon populations in the Baltic Sea seem to possess spatial and temporal differences in growth. This study suggests that these differences are explained by stock, dietary prevalence and water temperature.