Drought stress affects yield formation and quality of sugar beet. The aim of this study was to identify the growing period, in which drought stress has the greatest impact on growth, and furthermore, to analyze the response of differ-ent sugar beet genotypes. Causes for a different response should be identified. In pot experiments in the greenhouse, drought stress was simulated by reducing irrigation to 60% of the water holding capacity (WHC) for four weeks at various growth stages followed by rewatering. Growth reduction was greatest when drought stress occurred early in the season: the content of the quality-determining non-sugars was highest, sugar yield and beet diameter were lowest. Responses of the genotypes in sugar yield, but primarily in the accumulation of osmotically active substances differed. Despite rewatering after drought stress the restrictions could not be compensated during growth. The transpiration coefficient of the drought-stressed treatments was only slightly different to the control, because water consumption in the control did not either increase at average air temperatures beyond 23 °C. The strong effect of early drought stress could be attributed to the high growth rates, so that a limited water supply affected yield formation more than at later growth stages.