  We performed numerical simulations of stellar occultations by extra-solar
cometary tails. We find that extra-solar comets can be detected by the apparent
photometric variations of the central stars. In most cases, the light curve
shows a very peculiar ``rounded triangular'' shape. However, in some other
cases, the curve can mimic a planetary occultation. Photometric variations due
to comet occultations are mainly achromatic. Nevertheless, if comets with small
periastrons have smaller particles, these occultations could be chromatic with
a larger extinction in the blue by few percents.
  We also estimate the number of detections expected in a large photometric
survey at high accuracy. By the observation of several tens of thousand of
stars, it should be possible to detect several hundreds of occultation per
year. We thus conclude that a spatial photometric survey would detect a large
number of extra-solar comets. This would allow to explore the time evolution of
cometary activity, and consequently would probe structure and evolution of
extra-solar planetary systems.
