The morphology of melt-crystallized isotactic poly(4-methylpentene-1) samples, prepared by varying crystallization temperature and time, as well as annealing temperature, has been probed by small and wide angle x-ray scattering, and electron microscopy. This was then correlated with the thermal properties investigated by differential scanning calorimetry. Relationships among melting behavior, morphological evidences and X-ray results have been found. Different populations of lamellae, grown with a time-dependent sequence, can be obtained: their relative amount and thermal stability is determined by crystallization and annealing conditions.