While several studies have shown that genetically modified Bt cotton can benefit smallholder farmers economically, the sustainability of these effects is still unclear and debated controversially between biotechnology proponents and critics. We use unique panel data of 533 cotton farmers, collected in India between 2002 and 2008, to analyze Bt impacts on cotton yield, profit, and household living standards. Results from fixed effects models show that the adoption of Bt cotton is associated with a net yield gain of 24% and a profit increase of 50%.