Barley (Hordeum vulgare) grown in Mediterranean regions undergoes drought stress during the grain-filling period. A greenhouse experiment was conducted to study the effect of drought stress on grain growth and yield of barley. Plants were exposed to three drought treatments at the beginning of grain filling: (1) well-watered at 100% field capacity, (2) mild drought stress at 60% field capacity, and (3) severe drought stress at 20% field capacity until grain maturity. Grain moisture content and dry weight were determined for grains harvested at 3, 10, 17, 23 and 31 days after the beginning of grain filling. Grain dry weight for severe drought stress plants reached a maximum value earlier than grains from mild drought stress and well-watered plants, indicating that grains from severe drought stress plants had a higher growth rate than those of mild drought stress and well-watered plants. Drought-stressed plants had shorter duration of grain filling than well-watered plants. Drought stress treatments reduced grain yield by reducing the number of tillers, spikes and grains per plant and individual grain weight. In conclusion, postanthesis drought stress was detrimental to grain yield regardless of the stress severity.