Twenty-four hyperactive and 55 non-hyperactive children made a button press after the disappearance of a stimulus presented for either 1, 15 or 30 sec. Hyperactive children's responses were generally slower than those of non-hyperactive children and increased with length of pre-response delay, while non-hyperactive children's response time remained the same across all presentation levels. The results are interpreted as giving support to accounts that stress the role of pre-response delay, rather than time on task per se, as an important determinant of hyperactive children's attentional performance.