Electron diffraction patterns from solution polymerized single crystal whiskers ([100] and [010]) and confined thin film melt polymerized single crystal lamellae ([001]), in conjunction with modeling using Cerius [2], are used to determine the crystal structure of Phase I of poly(2,6-oxynaphthoate). the unit cell is triclinic (pseudo-monoclinic) a=7.712, b=5.905, c=17.202Å and β=97.5, α=γ=90°, space group P1. Comparison of observed and calculated structure factors yields an R-factor of 0.25, the relatively large value being attributed to whisker tilt and/or rotation and secondary scattering from the stacks of single crystal lammellae. parallel packing of the chains is proposed, in agreement with morphological observations. Other methods than the use of whiskers for obtaining 00L reflections (shearing in the liquid crystal state, shearing of the monomer and epitaxial polymerization/crystallization) are described: the use of nascent polymer gives rise to the most perfect crystals