The primary focus of the study is the changes that occurred in the pesticide-use structure of cotton production sector of India, owing to the diffusion of Bacillus thuringiensis (Bt) technology. Studies from different countries show that transgenic Bt crops can reduce chemical pesticide use with positive economic, environmental, and health effects. However, most of these studies build on cross-section survey data, so that longer term effects are uncertain. Bt resistance and secondary pest outbreaks may potentially reduce or eliminate the benefits over time, especially in developing countries where refuge strategies are often not implemented. Here, data from a unique panel survey of cotton farmers, conducted in India between 2002 and 2008, show that the Bt pesticide reducing effect has been sustainable. In spite of an increase in pesticide sprays against secondary pests, total pesticide use has decreased significantly over time. Bt has also reduced pesticide applications by non-Bt farmers. These results mitigate the concern that Bt technology would soon become obsolete in small farmer environments. The survey data on actual pesticide use in farmers’ fields complement previous entomological research.