Among the long period variable stars included in the Hipparcos observing program, 245 large-amplitude ones require brightness predictions during the mission in order to allocate the necessary observing time. We present the computation of the light ephemerides with numeric and symbolic methods using AAVSO’s 75-year data on maxima and minima dates and magnitudes and 20 years of individuai observations; the evaluation and revision of the ephemerides using ground-based observations compiled monthly by the AAVSO from observers world-wide and real-time monitoring of ephemerides stars from satellite observations performed at ESOC; the statistical results derived from one-and-a-half years of simultaneous ground-based and Hipparcos observations. We show the usefulness of all this work in understanding the physics of these pulsating variable stars.