The crystal structure and helical conformation of polybutene-1 crystallized from dilute solution is shown to be a function of the crystal structure before dissolution, the maximum temperature in solution attained before cooling to the crystallization temperature, and the time at that maximum temperature. The effect is, in general, reversible if the solution is held for sufficient time (on the order of 1 hr) before crystallization. The results suggest a temperature-dependent equilibrium helix conformation in solution, which only slowly approaches equilibrium and which determines the helical conformation of the resulting nuclei during crystallization. Solution viscosity measurements indicate a substantial difference in molecular size corresponding to the variation in thermal history. The results indicate that the prior history of a polymer may not be removed by solution.