The ultra-violet irradiation of O-acetyl-1-dehydro-2-methyl-testosterone (1) in dioxane solution leads to a mixture of ketonic and phenolic isomers from which five components (2–6) have been isolated. The structures of ketones 2 and 4 have been established. The sequence of photochemical rearrangements is1→2→3. Evidence points to the intermedi acyof an isomer of type e and the formation of compounds 4 and 5 from 3. Structural formulas for 3 (=g) and 5 (=j) are advanced on this basis. The close relationship between the sequences of rearrangements initiated by the irradiation of O-acetyl-1-dehydro-testosterone and its 2-methyl homologue (1), respectively, is discussed.