The recent introduction of the full Sharia, the Islamic legal system, by some Northern states in Nigeria raises a number of constitutional questions and impacts the supremacy of the Nigerian Constitution. The Constitution prohibits the promotion of religion by either the federal government or any of its components states and also provides for the freedom of religion and the right of all citizens to practice their religion. At the same time, any law enacted in the country that conflicts with the Constitution is void to the extent of its inconsistency. The application of the Sharia in Nigeria prior to its recent configuration was limited to civil matters. The paper examines the constitutionality of the unilateral extension of the Sharia to crimes, and the human rights and other implications of such extension.