Next Generation Access Networks (NGAs) are a challenge to regulators and operators insofar as they require large investments, there is a significant uncertainty about the ability to recover costs, and the choice of the appropriate regulatory regime is far from consensual. Regulatory authorities might want to seize the moment and reconsider mandatory vertical separation of telecommunication firms, without jeopardizing incentives to innovation and investment. This paper discusses the main elements of a possible test for the adequacy of network separation as a regulatory remedy. A sequential decision tree procedure with three questions is proposed: (1) "Is there significant market power in the provision of access under NGAs?"; (2) "Are there little vertical complementarities between services along the supply chain?"; and (3) "Is network separation a better regulatory tool than any other alternative?". A positive answer to all the questions implies that the regulator should consider network separation as a regulatory remedy.