  We present the earliest results of our NACO/VLT sparse aperture masking (SAM)
campaign to search for binarity in a sample of 60 O-type stars. We detect Delta
Ks < 5 mag companions for 20-25% of our targets with separations in the range
30-100 mas (typically, 40 - 200 A.U.). Most of these companions were unknown,
shedding thus new light on the multiplicity properties of massive stars in a
separation and brightness regime that has been difficult to explore so far.
Adding detections from other techniques (spectroscopy, interferometry, speckle,
lucky imaging, AO), the fraction of O stars with at least one companion is 85%
(51/60 targets). This is the largest multiplicity fraction ever found.
