  We present a statistical study of optical warps in a sample of 540 galaxies,
about five times larger than previous samples. About 40% of all late-type
galaxies reveal S-shaped warping of their planes in the outer parts. Given the
geometrical parameters and detection sensitivity, this result suggests that at
least half of all galaxy disks might be warped. We demonstrate through
geometrical simulations that some apparent warps could be due to spiral arms in
a highly inclined galaxy. The simulations of non warped galaxies give an amount
of false warps of $\approx$ 15%, while simulations of warped galaxies suggest
that no more than 20% of the warps are missed. We find a strong positive
correlation of observed warps with environment, suggesting that tidal
interaction have a large influence in creating or re-enforcing warped
deformations.
