The atomic and molecular structure of 1-methylnaphthalene C10H7-CH3 at 293 K was investigated using the X-ray diffraction method, Monochromatic radiation MoKx, lambda = 0.71069 Angstrom enabled determination of the scattered radiation intensity between S-min = 4pisinv(min)/lambda = 0.430 Angstrom(-1) and S-max = 4pisinv(max)/lambda = 14.311 Angstrom(-1). The curves of reduced radiation intensity were analysed by the pair functions method and by the reduction method of Blum and Narten. Good agreement between the theoretical and experimental functions was obtained on assuming the statistically most probable model of this molecule. The results permitted the determination of the intermolecular and intramolecular distances, the coordination numbers and the packing coefficient. The most probable binary radial correlation of molecules in liquid 1-methylnaphthalene was proposed. These results can be interpreted in terms of a simple model of local arrangement of molecules, which probably can be valid for a larger class of molecular liquids, i.e. weakly polar monosubstituted derivatives of naphthalene. (C) 2002 Elsevier Science B.V. All rights reserved.