For the last two years, Guantanamo Bay has been the object of heated discussions. The US administration's decision to detain suspected terrorists at the Guantanamo naval base has given rise to much concern. In marked contrast to the amount of criticism directed against this US policy, there has been very little debate about the legal basis for the US presence on Cuban soil, which can be found in two lease agreements signed in 1903. This lack of discussion is surprising, as Cuba has constantly claimed a right to terminate the agreements. On the occasion of the 100th anniversary of the two agreements, the present contribution assesses the various arguments advanced by Cuba. In addressing the controversy over the Guantanamo Bay lease agreements, it also sheds light on the more fundamental tension between the stability and flexibility of international treaties.