A survey was done by N.Bowie and G Jackson in 2003 for the General Register Office for Scotland to find the most common surnames in Scotland. Their findings showed that on a national basis their had been little change in surnames over the last 140 years. 1 in 8 surnames began with Mac/Mc. Their finds for the top 10 are :
If all spelling variations of MacDonald were used this would move into second place.