  The disc instability model (DIM) has been very successful in explaining the
dwarf nova outbursts observed in cataclysmic variables. When, as in
intermediate polars (IP), the accreting white dwarf is magnetized, the disc is
truncated at the magnetospheric radius, but for mass-transfer rates
corresponding to the thermal-viscous instability such systems should still
exhibit dwarf-nova outbursts. Yet, the majority of intermediate polars in which
the magnetic field is not large enough to completely disrupt the accretion
disc, seem to be stable, and the rare observed outbursts, in particular in
systems with long orbital periods, are much shorter than normal dwarf-nova
outbursts. We investigate the predictions of the disc instability model for
intermediate polars in order to determine which of the observed properties of
these systems can be explained by the DIM. We use our numerical code for the
time evolution of accretion discs, modified to include the effects of the
magnetic field, with constant or variable mass transfer from the secondary
star. We show that intermediate polars have mass transfer low enough and
magnetic fields large enough to keep the accretion disc stable on the cold
equilibrium branch. We show that the infrequent and short outbursts observed in
long period systems, such as e.g., TV Col, cannot be attributed to the
thermal-viscous instability of the accretion disc, but instead have to be
triggered by an enhanced mass-transfer from the secondary, or, more likely, by
some instability coupling the white dwarf magnetic field with that generated by
the magnetorotational instability operating in the accretion disc. Longer
outbursts (a few days) could result from the disc instability.
