  High-quality K-band spectra of point sources, deeply embedded in massive
star-forming regions, have revealed a population of 20 young massive stars
showing no photospheric absorption lines, but only emission lines. The K-band
spectra exhibit one or more features commonly associated with massive Young
Stellar Objects surrounded by circumstellar material: a very red color (J-K) =
2, CO bandhead emission, hydrogen emission lines (sometimes doubly peaked), and
FeII and/or MgII emission lines. The CO emission comes from a relatively dense
(~10^10 cm^(-3)) and hot (T ~ 2000-5000 K) region, sufficiently shielded from
the intense UV radiation field of the young massive star. Modeling of the
CO-first overtone emission shows that the CO gas is located within 5 AU of the
star. The hydrogen emission is produced in an ionized medium exposed to UV
radiation. The best geometrical configuration is a dense and neutral
circumstellar disk causing the CO bandhead emission, and an ionized upper layer
where the hydrogen lines are produced. We argue that the circumstellar disk is
likely a remnant of the accretion via a circumstellar disk.
