  We used the Revised Flat Galaxy Catalog (RFGC) to create a sample of
ultra-flat galaxies (UFG) covering the whole northern and southern sky apart
from the Milky Way zone. It contains 817 spiral galaxies seen edge-on, selected
into the UFG sample according to their apparent axial ratios $(a/b)_B\geq10.0$
and $(a/b)_R\geq8.53$ in the blue and red bands, respectively. Within this
basic sample we fixed an exemplary sample of 441 UFG galaxies having the radial
velocities of $V_{LG} < 10000$ km s$^{-1}$, Galactic latitude of $\mid
b\mid>10^{\circ}$ and the blue angular diameter of $a_B > 1.0^{\prime}$.
According to the Schmidt test the exemplary sample of 441 galaxies is
characterized by about (80-90)% completeness, what is quite enough to study
different properties of the ultra-flat galaxies. We found that more than 3/4 of
UFGs have the morphological types within the narrow range of $T= 7\pm1$, i.e.
the thinnest stellar disks occur among the Scd, Sd, and Sdm types. The average
surface brightness of UFG galaxies tends to diminish towards the flattest
bulge-less galaxies. Regularly shaped disks without signs of asymmetry make up
about 2/3 both among all the RFGC galaxies, and the UFG sample objects. About
60% of ultra-flat galaxies can be referred to dynamically isolated objects,
while 30% of them probably belong to the scattered associations (filaments,
walls), and only about 10% of them are dynamically dominating galaxies with
respect to their neighbours.
