We report on a multiplicity survey of a sample of X-ray selected young stars in the Chamaeleon association .
We used speckle-interferometry and direct imaging to find companions in the separation range 0.13 ^ { \prime \prime } to 6 ^ { \prime \prime } .
After correction for chance alignment with background stars , we find a multiplicity ( number of binaries or multiples divided by number of systems ) of ( 14.0 \pm 4.3 ) \% and a companion star frequency ( number of companions divided by number of systems ) of ( 14.7 \pm 5.1 ) \% .
Compared to solar-type main-sequence stars , the companion star frequency is lower by a factor of 0.61 \pm 0.27 .
This is remarkably different from the high multiplicity found in the Taurus-Auriga star-forming region and for T Tauri stars in Chamaeleon known before ROSAT .
We find only a few binaries with projected separations of more than 70 AU , also in contrast to the results for stars known before ROSAT .
This indicates that the X-ray selected stars belong to a different population than the stars known before ROSAT , a hypothesis further supported by their Hipparcos distances and proper motions .