The MULTIPLOT routine in the IDL Astronomy User's Library doesn't work in GDL, but here is a workaround.
Set the number of plots, and the [x,y] coordinates for the lower-left and upper-right boundaries of the plot area in device coordinates. Use the lower-left boundaries to leave room for axis titles.
nplots = 3 ll = [0.1,0.1] ur = [0.975,0.975]
The next two lines are examples for how to set the coordinates of the borders in between plots, for vertically-stacked plots. The bottom of the first plot is located at first and the bottom of the second plot is located at second.
first = (ur-ll)/nplots*(nplots-1) + ll second = (ur-ll)/nplots*(nplots-2) + ll
Then use the POSITION keyword to specify the lower-left and upper-right coordinates of each plot, as follows. Use the /NOERASE keyword for making the multiple plots, leaving !P.MULTI = 0. To have GDL still draw axes in between the plots, but not label the tick marks, use XTICKFORMAT="(A1)".
plot,xvalues,yvalues,position=[ll,first,ur,ur],xtickformat="(A1)",ytitle='Y Title 1' plot,xvalues,yvalues,position=[ll,second,ur,first],xtickformat="(A1)",/noerase,ytitle='Y Title 2' plot,xvalues,yvalues,position=[ll,ll,ur,second],/noerase,xtitle='X Yitle',ytitle='Y Title 3'