In order to exploit economies of scale Belgian municipalities regularly cooperate in the provision of waste related services. In particular for the collection and separation of household packaging waste, municipalities appear to seek technical and cost efficiency gains by cooperating via municipal waste joint ventures. Although most Belgian municipal waste joint ventures can present excellent recycling and recovery rates for household packaging waste, their performance in terms of cost-efficiency has never been assessed. Using a unique dataset comprising of the costs for all 35 Belgian municipal waste joint ventures in 2010, this paper present the first assessment of the cost efficiency of household packaging waste collection in Belgium. As we are not sure on the relative importance of the separate cost efficiency scores for the three selectively collected household packaging waste fractions when determining the overall cost efficiency, this paper draws on the Benefit-of-the-Doubt approach. Our results indicate that, despite the substantial cooperation between municipalities, still considerable differences in cost efficiency for household packaging waste collection exist.