Lamellar thickness and its distribution in high-density polyethylene (HDPE) films having a well-defined stacked lamellar morphology were investigated by using differential scanning calorimetry (d.s.c.), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). It was found that the most probable lamellar thicknesses from SAXS and TEM agrees very well; however, they do not agree with those values obtained from d.s.c. and AFM. It is pointed out that the use of d.s.c. as a tool to determine lamellar thickness and its distribution is so sensitive to the rate of heating in the d.s.c. experiments and the parameters in the Gibbs-Thomson equation that it is not believed to be suitable for routine quantitative analysis.