Most of the following is paraphrased from the introduction to Personal Names in Scotland (Edinburgh: GROS, 1991)
There have been five surveys to date, conducted by the Registrar General Scotland, into Personal Names in Scotland. The introduction to the current 1991 survey, outlines the historical background.
Main findings of surveys:
The 1858 report commented on the low proportion of different surnames in Scotland compared with England. Scotland had 15.2 persons for every surname; England 8.4 persons to every surname. Part of this was assumed to be due to the clan system of surnames. The report commented on "a striking peculiarity of the inhabitants of Scotland that, both among the Celtic race in the Highlands and the Lowland races on the border, it was the custom for all to assume as their surname the name held by the head of a family, either because they were actually his descendants, or because they were his vassals and property." But the 15.2 figure will be too high, as the 1858 survey combined different spellings of similar surnames into one generic name. "Mac", "Mc" and "M" were all treated as being "Mac".
The 1935 survey similarly combined forms, and found 11,976 surnames. (In actuality there would have been 14,666 without combining.)
The 1990 report discovered 19,108 surnames, resulting in a rate of 10.3 persons per surname. This 'increase' is not just due to the changing methodology, but also to the decline of clan naming, and also in-migration. The immigration began in 1820 and reached its peak in the 1840s due to the demand for railway labourers. The 1858 survey commented "in addition to to bringing over about 1,000 surnames which are common to Scotland and Ireland, they have added to the Scottish surnames nearly a thousand which till that period were peculiar to Ireland". Nonetheless, the 1858 survey concluded that 32 out of the top 50 names were deemed to both have originated in, and to be peculiar to Scotland. The remainder being equally common to England. None of the top 50, in 1858, was typically Irish. By 1935, the leading Irish name in the list was Kelly (at 47), with Docherty, Murphy and Gallacher in the next 50. By 1958, McLauglin and Boyle had been added to this list.
[Irish names in Scotland in 1881 - a possible area of research?]
A current list of the current leading 100 surnames in Scotland can be found at the General Register Office for Scotland (GROS) web site
The following table lists the top 50 surnames in Scotland, as ranked in the 5 previous surveys