  We present millimetre-line imaging of the Galactic HII region Sh 104. We show
that it is surrounded by a ring of molecular gas and dust. Four large molecular
condensations are regularly spaced around the ring. These condensations are
themselves fragmented and contain several massive dense cores. A deeply
embedded cluster is observed in the near IR towards the largest condensation.
It contains at least one massive star ionizing an ultra-compact HII region. The
Sh 104 region is a good illustration of the `collect and collapse' model for
star formation triggered by the expansion of an HII region.
