Single crystals of poly(naphthalic anhydride) (PNA) have been grown using our confined thin film melt polymerization technique. Lamellae, 70-100 Angstrom thick, are found for the crystals polymerized at 180 degrees C with thinner lamellae for a 200 degrees C polymerization temperature. In addition, irregular lath-shaped crystals are found for both polymerization temperatures, apparently formed by a solid-state polymerization process within the original needle-like monomer crystals. The crystal structure of PNA has been studied by electron diffraction (ED) and computer modeling based on seven different zonal ED patterns. It is found that, in most cases, two or three different zonal patterns are superimposed with a common plane, suggesting variable chain tilting even in individual lamellae. Shearing of the material shortly after the initiation of polymerization, permitted obtaining an additional [010] zone ED pattern. A monoclinic unit cell with one chain, two repeat units is proposed based on measurements of 21 independent reflections; the space group is Pc11; a = 6.26 Angstrom, b = 4.33 Angstrom, c 18.60 Angstrom, and alpha = 122.5 degrees. The computer-simulated (Cerius(2)) molecular conformation and chain packing are described with the corresponding simulated electron diffraction patterns being in good agreement with the observed ones.