The thermal properties and the crystalline structure of poly(methylenecyclopentane) samples with different microstructures are investigated. Similar disordered crystalline structures are formed, independently of the microstructure of the sample. These structures present hexagonal packing of the chain axes and extended chains with configurational and conformational disorder, which generate intermolecular rotational and translational disorder. The distance between adjacent parallel chains decreases with the increase of rings with the cis configuration; correspondingly, the melting temperature strongly increases. Both interchain distances and melting temperatures seem poorly dependent on the relative stereochemistry between rings. The degree of crystallinity and the correlation length of the crystalline domains tend to increase with the stereoregularity in the configuration of the rings (both cis and trans). The melting entropy increases with all the examined kinds of stereoregularity (cis, trans, and isotactic).