The isothermal crystallization of in-situ-polymerized and melt-processed nylon-6/montmorillonite nanocomposites was studied by simultaneous small- and wide-angle X-ray scattering using synchrotron radiation. The isothermal crystallization rates, in the nucleation-controlled regime, for the nanocomposites are significantly faster than that for the pristine nylon-6 and suggest that the layered silicates act as nucleating centers. Within the experimental resolution, the initial crystal phase formed between 185 and 205 degreesC in the presence of the layered silicate is the metastable gamma-phase, whereas the a-phase develops in the pristine nylon-6 at comparable temperatures. Additionally, the strong silicate-polymer interactions present in the in-situ-polymerized nanocomposites alter the crystallization process, creating a much weaker temperature dependence for the crystallization kinetics. Finally, the presence of well-dispersed layered silicates significantly disrupts the development of lamellar structure but does not alter the overall amounts of crystallinity.