Originally Posted by Cambo

Strange, nobody does raise this. BKK does have a trick to avoid the busy immigration and security areas.

For arrivals, BKK does have 3 (previously 2) arrival immigration processing areas. The majority of the big airplane international arrivals is on concourses EFG (West side). These people all tend to go to the first immigration area they encounter in concourse D, and it is nearly always busy there. Just walk further for 150m - 250m and there are 2 more arrival immigration processing areas. These are often deserted. The priority arrival immigration processing seems to have been reduced to only one bigger area, in the middle processing area, which is nearly always busy, unfortunately.

For departure, the majority of people tend to go to the "central" departure immigration processing area, whereas the (somewhat smaller) one at the West side of the Terminal is usually quiet.

So, how long one has to wait largely depends on which processing area the passenger select. Be smart and one usually flies through.