Since the restoration of civilian rule in Nigeria in 1999, the governments of various Northern states have initiated reforms designed to remodel their legal systems in conformity with the Sharia. An issue which has generated intense controversy, especially in legal and political circles, is whether these reforms are consistent with certain key provisions of the 1999 Constitution. This study begins by tracing the historical process through which the application of the Sharia has emerged as a matter of profound constitutional importance in Nigeria. This is followed by a detailed analysis of specific provisions of the 1999 Constitution which are considered to have a direct bearing on the constitutionality of the Sharia reforms. Particular attention is paid to those provisions which proclaim the supremacy of the Constitution, prohibit the adoption of a state religion and prescribe the jurisdiction of various courts. Consideration is also given to the effect of various fundamental rights guaranteed by the Constitution on the Sharia penal regimes introduced as part of the reforms. The study demonstrates that various facets of the reforms are difficult to reconcile with the 1999 Constitution and concludes that fundamental constitutional reforms will be required to redress this state of affairs.