Synthesis of CePO4 in water-in-oil microemulsions produces crystalline nanowires with uniform thickness (mean width = 3.7 nm) and straight or branched morphologies. The nanowires develop within a period of 1 month by surfactant-mediated slow crystallization from amorphous primary filaments with highly convoluted morphology. Electron microscopy and dynamic light scattering studies suggest that CePO4 crystallization occurs within the confined reaction spaces of preformed Ce(III)-containing rod-shaped micelles, rather than by mesophase aggregation and transformation of primary surfactant-coated nanoparticles.