The crystal structure of fluvoxamine hydrogen maleate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Fluvoxamine maleate crystallizes in space group P21/c (#14) with a = 21.6310(15), b = 5.3180(4), c = 19.5555(15) Å, β = 99.979(5)°, V = 2,215.48(25) Å3, and Z = 4 at 298 K. The crystal structure consists of alternating double layers of cations and anions parallel to the bc-plane. Hydrogen bonds link the layers of anions and cations parallel to the bc-plane. The powder pattern has been submitted to the International Centre for Diffraction Data for inclusion in the Powder Diffraction File™ (PDF®).