This dataset comprises available archived information (1963-2023) on returning adult Atlantic salmon size and age derived both from long-term monitoring programs operating over decades and shorter-term ad-hoc efforts operating sporadically in rivers throughout Scotland. Individual adult Atlantic salmon were captured in commercial or recreational fisheries on their return to fresh water, within scientific net fisheries, or in traps designed to capture salmon migrating upstream. The sampling locations were in mid to lower reaches of rivers. Biological characteristics (fork length to nearest 0.5 cm, weight) of each individual were recorded, and a scale sample was taken from the flank of the fish. Scales were impressed in acetate and interpreted by an experienced salmon scale reader, to derive the number of years spent in fresh water (S1 = 1 year; S2 = 2 years; S3 = 3 years) and at sea (1SW = 1 year; 2SW = 2 years; 3SW = 3 years). Individuals assumed to be of farmed origin due to the pattern of scale growth, or with obvious spawning marks on the scales were excluded.