Here is some quick example code :
LOCAL a$,a%
a$=""
FOR a%=1 TO 100
INC a$,a%+"|"
NEXT
DDgui_pushdialog(0,0,319,100)
DDgui_combo("a",LEFT$(a$,LEN(a$)-1),319-8,100-24)
WHILE TRUE
DDgui_show(FALSE)
SHOWSCREEN
WEND
If run in 320 x 240 or so, you can see that the scrollbar area is partially off the screen