  Magnetic chemically peculiar (mCP) stars of the upper part of the main
sequence usually exhibit strictly periodic variations of their light, spectrum
and magnetic field. These changes can be well explained using the oblique
rotator model of the rigidly rotating star with persistent photometric spots,
uneven horizontal abundance of chemical elements and dipole-like magnetic
field. Long-term observations of mCP stars variability enable to determine
their rotational periods with an extraordinary accuracy and reliability. We
compare rotational periods of mCP stars with those of normal main sequence
stars of the same spectral type and discuss the found discrepancies. We also
discuss the cases of mCP stars V901 Ori, SX Ari, CU Vir, (and possibly also EE
Dra), which have been reported to display an increase of their rotational
periods.
