Farmers in Pakistan have been growing cotton that contains the first generation of Bt gene since 2002. The cultivation of these varieties, although formally unapproved and unregulated, increased rapidly after 2005. In 2007, nearly 60 percent of the cotton area was under BT varieties. This paper examines the economic performance of Bt cotton in Pakistan based on data collected through a structured questionnaire survey in January-February 2009 in two districts (Bahawalpur and Mirpur Khas). The extent of the impact of Bt cotton on costs of production and yield gains are different across the two districts with their diverse agro-climatic conditions and pest pressures. Seed expenditures increase in both districts, but a decline in the number of bollworm sprays and hence in the expenditure for pesticides is observed and total pesticide control costs (for bollworms and non bollworm pests) declines in both districts. Total production costs decline in Bahawalpur but rise in Mirpur Khas. The yield increases are higher in Mirpur Khas as well, resulting in total revenue and gross margins improving more than in Bahawalpur. The results are similar to other studies of Bt cotton in India and suggest gains for Pakistan from progressing to a regulated national market for Bt cotton technologies.