Web search query data were found to be capable of tracking dengue activity in Bolivia, Brazil, India, Indonesia and Singapore. Whereas traditional dengue data from official sources are often not available until after some substantial delay, web search query data are available in near real-time and could serve as a useful low-cost complement to traditional surveillance. Even if peaks are no earlier, there is value in 'nowcasting'*predicting the present where there are delays in gaining access to current official data (5) . More broadly, these results also contribute to a growing pool of evidence demonstrating the capability of relatively novel sources such as webbased data to assist with public health goals. The product of this work is freely available at www.google.org/denguetrends. 