Single crystals of trans-1, 4-polyisoprene (TPIP) have been grown from dilute solutions in amyl acetate, n-heptane and n-butanol/n-heptane mixtures. Two samples of different molecular weights, and molecular-weight distribution have been used to demonstrate the effect of these molecular parameters on the shape of single crystals. The experiments suggested that crystallization of narrowly distributed polymer chains, irrespective of the molecular weight of the crystallizing species, will produce a hexagonal morphology. This narrow distribution of chains during crystallization can be achieved by starting with a sample of low polydispersity or using a solvent/non-solvent mixture for crystallization. If the chain-size distribution is not controlled, then at later stages of growth the heterogeneous mixture of chains will create a curvature on the {110} faces and produce oval-shaped lamellar platelets. Further, the crystal habits in the present work were found to be related to the solvent, molecular weight and molecular-weight distribution, rather than to the crystallization temperature.