Bioretention cells have been found to improve the hydrologic and water quality performance of impervious areas such as parking lots. The current study recorded hydrologic data from a bioretention cell in Silver Spring, MD, over a period of 2 years, collecting water quality data from 14 storm events. Data showed the cell completely captured storm events that produced less than or equal to 1.27 cm of rainfall, after which a linear relationship between cell outflow and cell inflow was observed. The cell was found to reduce the site CN from 96 down to 79 and to have a CN of 96 when assessed as a separate land use. The hydrologic performance was also compared to that of a forested stream near Baltimore, MD. While the cell performed similarly volumetrically for storms producing less than or equal to 2 cm of rainfall, the Sligo-Dennis flow-durations were typically half the length and double the flowrate of those of the forested stream.