  A sample of O- and B-type stars with Hipparcos astrometric data, ages
computed from Str\"omgren photometry and radial velocities, has been used to
characterize the structure, age and kinematics of the Gould Belt system. The
local spiral structure of our galaxy is determined from this sample, and also
from a sample of Hipparcos Cepheid stars.
  The Gould Belt, with an orientation with respect to the galactic plane of
$i_{\mathrm{G}} = 16$-$22^\circ$ and $\Omega_{\mathrm{G}} = 275$-$295^\circ$,
extends up to a distance of 600 pc from the Sun. Roughly the 60-65% of the O
and B stars younger than 60 Myr in the solar neighbourhood belong to this
structure. Our results indicate that the kinematical behaviour of this system
is complex, with an expansion motion in the solar neighbourhood ($R <$ 300 pc).
  In the frame of the Lin's theory, and analysing the O and B stars further
than 600 pc and the Cepheids, we found a galactic spiral structure
characterized by a 4-arm spiral pattern with the Sun located at $\psi_\odot =
350$-$355 \pm 30^\circ$ -- near the Sagittarius-Carina arm -- and outside the
corotation circle. The angular rotation speed of the spiral pattern was found
to be $\Omega_{\mathrm{p}} = 31$-$32 \pm 4$ km s$^{-1}$ kpc$^{-1}$.
