  We present a comparative study of the circumstellar disks in Be/X-ray
binaries and isolated Be stars based upon the H-alpha emission line. From this
comparison it follows that the overall structure of the disks in the Be/X-ray
binaries is similar to the disks of other Be stars, i.e. they are axisymmetric
and rotationally supported. The factors for the line broadening (rotation and
temperature) in the disks of the Be stars and the Be/X-ray binaries seem to be
identical.
  However, we do detect some intriguing differences between the envelopes. On
average, the circumstellar disks of the Be/X-ray binaries are twice as dense as
the disks of the isolated Be stars. The different distribution of the Be/X-ray
binaries and the Be stars seen in the full width at half maximum (FWHM) versus
peak separation diagram indicates that the disks in Be/X-ray binaries have on
average a smaller size, probably truncated by the compact object.
