  We have conducted a systematic search for multiperiodic pulsations in the RR
Lyrae-type stars of the galactic globular cluster Omega Cen. Secondary
periodicities close to the primary pulsation frequency have been detected in 17
out of 70 studied fundamental mode (RRab) pulsators and in 35 out of 81
overtone (RRc) pulsators. Because of the observed period ratios, these newly
detected periodicities must correspond to nonradial modes. Their beating with
the primary radial pulsation leads to a slow amplitude and phase modulation,
commonly referred to as the Blazhko effect. The incidence rate of Blazhko
modulation in Omega Cen RRab stars (24 +/- 5%) is similar to that observed in
the Galactic Bulge. In the case of Omega Cen RRc stars, the incidence rate of
Blazhko effect is exceptionally high (38 +/- 5%), more than 3 times higher than
in any other studied population.
  In addition to Blazhko variables, we have also identified two RR Lyr
variables exhibiting first overtone/second overtone double-mode pulsations, and
a triple-mode High Amplitude Delta Scuti variable.
