Polychlorotrifluoroethylene (PCTFE), crystallized in two degrees of crystallinity, was subjected to tensile stress deformation experiments at several strain rates and temperatures in an attempt to relate the macroscopic deformation and failure characteristics of the polymer with its molecular organization and segmental mobility. At 3K, the higher crystallinity samples exhibited a higher tensile modulus, yield stress and a lower elongation to failure than lower crystallinity samples. At 78k and 4.2K, the lower crystallinity samples showed higher tensile moduli yield stress, stresses at failure and elongations to failure than did the higher crystalline samples. Sequential still photographs of the deforming sample were taken in the 3K experiments to determine the true-stress vs. true-strain curve for PCPFE. Fracture surfaces were examined with a scanning electron microscope to determine the mode of fracture. PCTFE appears to fail in a five-step process at 3K, in a three-step process at 78K and in a two-step process at 4.2K.