The title compound, C(11)H(23)NO(5)P(+)·I(-), consists of an eight-membered cationic heterocyclic ring in a boat-chair conformation. The ring features a tetra-alkyl-ammonium N and a methyl-phospho-nate P atom. A -CH(2)(CO)OC(2)H(5) ester side chain at the C adjacent to oxygen produces two chiral centers at that substituted C atom and the P atom, both of which were determined to have absolute R,R configurations. A previously determined racemic bromide analog has exactly the same ring but with a -C(15)H(31) side chain. In that structure, both chiral centers show the same relative R/S,R/S configurations, but the ring in the bromide analog is in a boat conformation.