A better understanding of green roof stormwater performance is needed to assess and predict benefits of proposed green roof projects. A nine-month green roof pilot study was conducted in mid-Missouri to evaluate runoff quantity and quality under field conditions for two different media, both tested under planted and unplanted conditions. Water quantity results showed a ~40% reduction in runoff from the unplanted growing media and a ~60% reduction in runoff from the planted growing media. A water balance model was developed that incorporated water storage in the media and evapotranspiration (ET) from the media based upon local weather conditions using the Penmen-Monteith ET method. Water quality monitoring showed a first-order decline of excess nutrients in the first few months of green roof operation. Total phosphorus > 30. mg-P/L and total nitrogen concentrations >60. mg-N/L were observed in green roof runoff initially, with concentrations decreasing over nine months to ~5. mg-P/L and ~10. mg-N/L, respectively. In addition, elevated total organic carbon concentrations were observed, with concentrations of 500. mg/L initially, decreasing after a few weeks to below 50. mg/L. Media type and age were the largest influences on carbon and nutrient loading from the green roof media tested.