In 4-chloro-7-(2-deoxy-beta-D-erythro-pentofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamine, C11H14ClN5O3, the conformation of the N-glycosylic bond is between anti and high-anti [chi = -102.5 (6) degrees]. The 2'-deoxyribofuranosyl unit adopts the C3'-endo-C4'-exo (3T4) sugar pucker (N-type) with P = 19.6 degrees and taum = 32.9 degrees [terminology: Saenger (1989). Landolt-Börnstein New Series, Vol. 1, Nucleic Acids, Subvol. a, edited by O. Madelung, pp. 1-21. Berlin: Springer-Verlag]. The orientation of the exocyclic C4'-C5' bond is +ap (trans) with a torsion angle gamma = 171.5 (4) degrees. The compound forms a three-dimensional network that is stabilized by four intermolecular hydrogen bonds (N-H...O and O-H...N) and one intramolecular hydrogen bond (N-H...Cl).