We analyse vertical integration between generators and retailers in electricity markets and we discuss the implications for price decisions of the presence of asymmetric (cost) information in a simple P-A framework. We analyze a situation in which generators post supply bids taking into account the profit of the entire vertically integrated group they belong to. We then discuss the way in which the degree of vertical integration affects this bidding strategy. Using Italian electricity auction data we show how bid prices posted by a pivotal producer are significantly influenced by variables incorporating vertical integration into the econometric model.