In view of its potential for developing useful pharamaceutical formulations of furosemide, a widely-used loop diuretic, the crystal structure of the furosemide anion with m-chlorobenzoate has been investigated. In these co-crystals, the monoanions of furosemide and m-chlorobenzoate are balanced by two independent Na+ ions, both of which are hexacoordinated by three monodentate water molecules, two double-water bridge molecules and one single-water bridge molecules, thus yielding centrosymmetric Na2(OH2)8 units linked by single water bridges to form chains in the [10] direction.