To enable cities to become more circular, i.e. close material cycles, decision-makers need detailed data about the production and treatment of waste. At city level, conventional statistics on waste are often incomplete or lack detail. Waste input-output accounting offers an alternative, using waste supply and use tables to create detailed inventories of economy-wide flows of waste. In this study we develop such tables for the city-region of Brussels (Belgium) and use them to analyse the urban waste metabolism in terms of waste flows, waste production intensity and waste treatment performance. The waste flow analysis revealed: the amount of collected waste; the proportion contributed by individual sectors; the material composition of waste flows and the location of treatment. Currently, around 50% of the 1.5 million tons of waste collected in Brussels is treated in local facilities. However, less than 1% of the collected waste is used in a way that closes material cycles within city limits. The waste performance analysis reveals that the construction sector had the highest waste production intensity and the household sector the highest incineration intensity. In terms of waste prevention and local valorisation potential, we identified flows and sectors for future targeting, one of the most promising being food waste. We conclude that the urban context can restrict the local valorisation of waste flows, thus we see the role of cities such as Brussels in a circular economy as mainly contributing to the closing of material cycles at national or even global level.