  The local velocity field of young stars is dominated by the galactic
rotation, the kinematics of the Gould Belt and the nearest OB associations and
open clusters, and the kinematics of the spiral structure. We re-examined here
this local velocity field by using a large sample of nearby O and B stars from
the Hipparcos Catalogue. The high quality astrometric data are complemented
with a careful compilation of radial velocities and Str\"omgren photometry,
which allows individual photometric distances and ages to be derived. The Gould
Belt extends up to 600 pc from the Sun with an inclination with respect to the
galactic plane of $i_{\mathrm{G}} = 16$-$22\degr$ and the ascending node placed
at $\Omega_{\mathrm{G}} = 275$-$295\degr$. Approximately 60% of the stars
younger than 60 Myr belong to this structure. The values found for the Oort
constants when different samples selected by age or distance were used allowed
us to interpret the systematic trends observed as signatures induced by the
kinematic behaviour of the Gould Belt. The contribution of Sco-Cen and Ori OB1
complexes in the characterization of the expansion of the Gould Belt system is
also discussed. We found that a positive $K$-term remains when these aggregates
are excluded. From the kinematic behaviour of the stars and their spatial
distribution we derive an age for the Gould Belt system in the interval 30-60
Myr.
