  We present a sample of 17 type 2 Seyfert galaxies which have an X-ray column
density lower than 10^{22} cm^{-2}. The Compton thin nature of these sources is
strongly suggested by isotropic indicators. We estimate the fraction of these
sources to be in the range of 10% - 30% of the population of type 2 Seyfert
galaxies. Furthermore, this fraction appears to increase progressively at lower
luminosities. The simple formulation of the Unified Model for Seyfert galaxies
is not applicable in such sources since the pc-scale molecular torus is not
likely to be responsible for the low column density observed, instead the
absorption observed is likely to originate at larger scales. According to this
hypothesis, in these objects the broad line regions are covered by some dusty
obscuring material. In particular, this could occur in objects with dust lanes,
patches or HII regions. However, we cannot rule out that in the lowest
luminosity sources the BLR is weak, absent or has faded away. This last
scenario is consistent with the predictions of some recent theoretical models
for low luminosity AGNs.
