  When a planet occults a spotty area on a stellar surface, the flux increases
and a characteristic feature in a light curve - a bump - is observed. Among the
planets detected by the CoRoT-mission CoRoT-18 is especially interesting as it
exhibited spot crossings that we have analysed in detail. We used four
ground-based observations obtained at a 1.5-m telescope in Spain and the 13
available CoRoT-transits to refine and constrain stellar, planetary and
geometrical parameters of the system. We found that the derived physical
properties slightly deviate from the previously published values, most likely
due to the different treatment of the stellar activity. Following a spot over
several transits enabled us to measure the stellar rotation period and the
spin-orbit alignment. Our derived values of Prot=5.19 +/- 0.03 d and Lambda=6
+/- 13 deg are in agreement with the literature values that were obtained with
other methods. Although we cannot exclude a very old age for CoRoT-18, our
observations support the young star hypothesis and, hence, yield constraints on
the time-scale of planet formation and migration.
