Single crystals of poly(terephthalic anhydride) (PTA) have been grown using the confined thin film melt polymerization technique. Thin lamellae (ca. 50 Angstrom) are found for low polymerization temperatures, with thick crystals forming for polymerization at 200 degrees C. Shearing of the material shortly after the initiation of polymerization at 200 degrees C yielded single crystal domains composed of fibrillar texture material; these samples gave [010] zone ED patterns complementing the [001] zone patterns from the unsheared CTFMP samples. A monoclinic, single chain, two repeat unit, unit cell (Pc11) is proposed based on four different electron diffraction zone patterns : a = 6.01 Angstrom, b = 3.94(5) Angstrom, c = 14.11 Angstrom, alpha = 106.9 degrees. Simulations, using the Cerius(2) program, of the corresponding molecular conformation, packing and electron diffraction (ED) patterns were performed; the ED simulations are in good agreement with the observed patterns. An R-factor of 0.23 is obtained based on a comparison of calculated and observed structure factors for the 39 independent ED reflections observed on the different zone patterns.