The structure of the title compound, pentoxifylline, C(13)H(18)N(4)O(3), has been previously characterized as a triclinic polymorph [Pavelčík et al. (1989 ▶). Acta Cryst. C45, 836-837]. We have discovered the monoclinic form. There are no strong hydrogen bonds in the crystal structure, rather, moderate C-H⋯O hydrogen bonds are present, which serve to stabilize the three-dimensional architecture.
