The photometric behaviour of 21 Ap stars has been analyzed from observations obtained in the Geneva system. Variability has been detected for 9 Ap stars, as well as for a star which initially was a comparison star. Preliminary values for the periods are presented as well as an analytical description of the light curves. The material has been collected during a 23-night observing run at La Silla with the 70cm telescope of the Geneva Observatory equipped with the standard Geneva photometer. The parameters of a second-order cosine fit to the lightcurves are stored in the accompanying table. Time origin is JD 2450000.0. The 17 phase diagrams for each of the 9 stars are presented in 9 postscript files. The observational data are superimposed on the Fourier fit. Data are differential, except for HD 191439 and HD 192674 which had no suitable comparisons.