The isothermal lamellar thickening behavior of a linear polyethylene fraction was investigated using differential scanning calorimetry. Experimental results indicate very similar evolutions for both the degree of crystallinity and the resulting apparent melting temperature with isothermal crystallization time. Deconvolution of the primary and secondary crystallization processes was carried out numerically using the classical logarithmic law for lamellar thickening. Reliability of the deconvolution process was investigated using artificial data generated using the Avrami kinetic law for the development of primary crystallinity. We show that the shift of the apparent melting temperature with time can be quantitatively accounted for by the intrinsic rates of primary crystallization and lamellar thickening. We also show that use of a single kinetic parameter for secondary crystallization is sufficient to account for the change in both the degree of crystallinity and the apparent melting temperature as a function of crystallization time.