Solution-grown lamellar crystals of poly(p-dioxanone) (PPDX) have been crystallized isothermally from butane-1,4-diol at 100degreesC. The crystal structure of PPDX has been determined by interpretation of X-ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge-shaped chain-folder lamellar crystals. The unit cell of PPDX is orthorhombic with space group P2(1)2(1)2(1) and parameters: a = 0.970 nm, b = 0.742 nm, and c (chain axis) = 0.682 nm. There are two chains per unit cell, which exist in an antiparallel arrangement.