The accepted theory of the provincial affiliation of the Aegean islands, going back to the work of F. Hiller von Gaetringen, is that all the islands included in the Diocletianic prouincia insularum had formed a part of the province of Asia ever since its organisation by Manius Aquillius in 129–126 BC. In this article it is argued that it cannot apply to for the islands not mentioned as part of the prouincia Asia in the Geography of Ptolemy (with the possible exception of Andros) for the period before the mid-2nd century AD. when the procuratorial district of Caria et Cyclades appears. It is suggested that this change occurred in the reign of Hadrian, who is known to have made other territorial adjustments in the region and, therefore, should be considered separately from the reforms of the organisation of Asia that took place under Marcus Aurelius. The importance of this conclusion for our assessment of Ptolemy’s data is emphasized.