  We present JHK observations of 22 intermediate-mass stars in Sco OB2,
obtained with VLT/NACO. The survey was performed to determine the status of
(sub)stellar candidate companions of A and late-B members. The distinction
between companions and background stars is by a comparison with isochrones and
statistical arguments. We are sensitive to companions in the separation range
0.1''-11'' (13-1430 AU) and K<17. We detect 62 secondaries of which 18 are
physical companions (3 new), 11 candidates, and 33 background stars. The
companion masses are in the range 0.03<M<1.19 Msun, with mass ratios
0.06<q<0.55. We include in our sample a subset of 9 targets with multi-color
ADONIS observations from Kouwenhoven et al. (2005). In the ADONIS survey
secondaries with K<12 were classified as companions; those with K>12 as
background stars. Our multi-color analysis demonstrates that the simple K=12
criterion correctly classifies the secondaries in ~80% of the cases. We
reanalyse the total ADONIS/NACO sample and conclude that of the 176
secondaries, 25 are physical companions, 55 are candidates, and 96 are
background stars. Although we are sensitive and complete to brown dwarfs as
faint as K=14 in the separation range 130-520 AU, we detect only one, giving a
brown dwarf companion fraction of 0.5% (M>30 MJ). However, the number of brown
dwarfs is consistent with an extrapolation of the stellar companion mass
distribution. This indicates that the physical mechanism for the formation of
brown dwarfs around intermediate mass stars is similar to that of stellar
companions, and that the embryo ejection mechanism does not need to be invoked
in order to explain the small number of brown dwarf companions among these
stars.
