  We present the results of a recent near-infrared survey of the fields
surrounding a large sample of intermediate-mass pre-main-sequence (Herbig
Ae/Be) stars. While late-type Be and Ae stars are never associated with
conspicuous groups of young lower mass stars, early-type Be stars are usually
found within rich clusters. This finding has been tested against possible
biases due to different mass sensitivity of the observations or dynamical
dissipation of the clusters around older stars. Our results suggest that
massive stars are preferentially produced in dense stellar clusters, possibly
by dynamical interaction rather than by standard gas accretion as in the case
of lower mass stars. The possibility that the observed correlation between
maximum stellar mass and cluster richness could be the results of random
sampling the cluster size spectrum and the stellar IMF is also discussed.
Future observational tests capable of discriminating between these two
competitive models are outlined.
