C21H29C1NO5P, Mr=441.89, monoclinic, P21, a = 13.8421 (11), b = 8.3808 (6), c = 9.8118 (9)A, B= 99.672 (7) °, v= 1122.1A 3, z = 2, D x = 1.308 Mg m -3. Cu Ka radiation (graphite-crystal monochromator, 2 = 1.54178 A), /~(Cu Ka) = 2.464 mm -1, F(000) = 468, T = 290 K, final conventional R factor=0.043, wR =0.057 for 3259 'observed' reflections and 348 variables. The structure contains phosphorinane cations and ephedrine anions which are linked in a three-dimensional network by N-H...O and O-H...O hydrogen bonds. The phosphorinane ring is in the usual chair conformation. The ephedrine is in the usual extended form. Related 1,3,2-dioxaphosphorinane and ephedrine compounds are compared.