Betamethasone (I, R = OH, R1 = H) was prepd. in high yield from 16.beta.-methyl-17-hydroxypregna-1,4,9(11)-triene-3,20-dione (II). Dehydrobromination of 16.beta.-methyl-9-bromo-11.beta.,17-dihydroxypregna-1,4-diene-3,20-dione, prepd. from the reaction of II with AcNHBrHClO3, gave the corresponding 9.alpha.,11.alpha.-epoxy steroid which with HF-DMF gave I (R = R1 = H). Diiodination of I (R = R1 = H) with iodine in the presence of CaO and CaCl2 gave I (R = R1 = I). The diiodo steroid was treated with KOAc to give betamethasone acetate (I, R = OAc, R1 = H) which was hydrolyzed to I (R = OH, R1 = H).