In the last 20 years, several crops such as oil seed rape and cereals have developed sulphur deficiency symptoms with subsequent yield reductions due to decreasing S deposition. The study aimed at (1) defining indicators for the S status of sugar beet and at (2) determining threshold values of internal S concentrations which affect yield and quality. For this purpose, the effect of S supply on S concentration and N/S ratio in leaves and on yield and technical quality of sugar beet was analysed. A field survey with 200 sites was conducted and S treatments were performed in 33 field trials and 4 pot experiments. In the field survey, the mineral S content in soil in spring did not affect S concentration in sugar beet leaves in July. In accordance, there was no effect of S application on yield and quality of sugar beet in the field trials, indicating that S was available in sufficient amounts. In pot experiments, beet yield and sucrose concentration decreased, while potassium, sodium and amino N concentration in the beet considerably increased with extremely low S supply. With S concentrations above 0.3 % (range of 0.28 to 0.32 %) in young leaf blades, which equalled N/S ratios below 20, no changes in yield or quality occurred as a result of S application, indicating that the plants were adequately supplied with sulphur. Plants from field trials and pot experiments reached maximum yields with the same S concentrations in the leaf blades. This good agreement leads to the conclusion that these threshold values do not depend on growing conditions and are therefore a general characteristic for sugar beet. S concentration and N/S ratio in the blades of young sugar beet leaves sampled in July are thus suggested as suitable indicators for the plant’s S status.