As advances in technology allow for the collection, storage, and analysis of vast amounts of data, the task of screening and assessing the significance of discovered patterns is becoming a major challenge in data mining applications. In this work, we address significance in the context of frequent itemset mining. Specifically, we develop a novel methodology to identify a meaningful support threshold s for a dataset, for which the number of itemsets with support at least s yields a substantial deviation from what would be expected in a random dataset with the same number of transactions and the same individual item frequencies. These itemsets can then be flagged as statistically significant with a small false discovery rate. Our methodology hinges on a Poisson approximation; we show that the distribution of the number of itemsets with Harvard School of Engineering and Applied Sciences, Cambridge, MA, USA. Email: kirsch@eecs.harvard.edu. Supported in part by NSF Grant CNS-0721491 and a...