Observations show that for massive stars the binary frequency seems to be higher than for lower mass stars in young dense clusters. This suggests that in clusters like the ONC different mechanisms are at work in the formation of high-mass binary or multiple systems than for low-mass stars. We investigate the stellar dynamics in young dense clusters to determine the role of capture in binary formation in high-mass stars. It turns out that in contrast to lower mass stars capture is a frequent process for massive stars. However, this does not necessarily lead to long lasting binary systems but is often of transient nature. Nevertheless, capture processes could account for 15-25% of the observed ‘binaries’ of the OB-stars (75%) in Orion.