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Distribution of precipitation event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosystem dynamics in these regions. Our objective Cor this Paper was to present a comprehensive analysis of the daily precipitation regimes of arid and semi-arid locations of the United States. We collected 30 years of daily precipitation and temperature data from 289 sites in the intermountain zone and 240 sites in the Great Plains for our analysis. The daily precipitation regimes at all sites were dominated by the smallest event sizes and the shortest intervals between events. Great Plains sites on average had more small events and more short interval, than sites in the intermountain zone. In both regions. small events and short intervals were significantly negatively correlated to all other sizes suggesting they were useful for characterizing precipitation regimes. Both the smallest precipitation events and the shortest intervals between precipitation events increased as mean annual temperature decreased. Small events were negatively, but short intervals were positively related to mean annual precipitation. Additional analysis of Great Plains data suggested both quantitative and qualitative differences between precipitation regimes in wet and dry climates. These differences are attributable in large part to the differences in the relationship between precipitation and the evaporative demand of the atmosphere between the semi-arid and sub-humid portions of the Great Plains. Copyright (C) 2009 John Wiley & Sons. Ltd.