The structural order of poly(vinyl chloride) (PVC) has been investigated using modified PVC samples. A lack of order in the polymer chain direction is evidenced by comparison between the experimental and the theoretical crystalline wide-angle scattering pattern of PVC. Variation of the molecular structure by specific substitution of chlorine proves to be a very useful tool to acquire some additional information with respect to the structural order of PVC. In this way, it is demonstrated that the isotactic sequences disturb the formation of structural order but do not totally exclude it. The structural order of PVC is preferentially ordered perpendicular to the polymer backbone and consists of short primarily syndiotactic sequences, belonging to different polymer chains or chain segments. The wide variety of size and perfection of these ordered entities as well as the lack of order in the polymer chain direction signifies that the term ''crystallinity'' in the case of PVC has to be used with some prudence.