The crystallization characteristics of poly(L-lactide) (PLLA) films of different molecular weights have been studied by differential scanning calorimetry, optical microscopy and a depolarized-light intensity (d.l.i.) method. In non-isothermal crystallization modes from the isotropic melt, the crystallinity of PLLA films increased remarkably with a decrease in the cooling rate, accompanied by a kind of annealing effect. Overall isothermal crystallization rates of the polymer determined by d.l.i. in the range from 90 degrees C to 140 degrees C indicated the maximum value at 105 degrees C. This temperature is lower than that (120 degrees C) at which the maximum spherullite growth rate is observed. The PLLA polymer exhibited an Avrami exponent n = 4 in the isothermal d.l.i. experiments over the whole temperature range examined. Molecular parameters governing the isothermal crystallization behaviour have been estimated by the application of secondary nucleation theory.