Reaction of thiirane 1,1-dioxide (1) with aqueous barium hydroxide gives chiefly barium ethanesulfonate (3) together with some ethylene and barium sulfite, and only a small amount (<5%) of barium 2-hydroxyethanesulfinate (2), the material previously described by Hesseetal. as the major product of this reaction. Reaction of1with potassium hydroxide proceeds analogously except for the formation of barium 2-sulfinatoethanesulfonate (6) from reaction of potassium sulfite with unreacted1. This revision, when taken with what is already known of the final step of the Ramberg–Bäcklund reaction, provides a consistent picture of the reaction of thiirane 1,1-dioxides with hydroxide. For this reaction we suggest a common intermediate with a pentacoordinated sulfur for formation of both the sulfonate anion and the olefin, though an attempt to confirm the existence of such a species using H218O was unsuccessful.