Many stormwater management manuals and guidance documents have stated the importance and estimated the necessary frequency of maintenance for stormwater best management practices (stormwater BMPs), but few have been able to document the actual frequency and intensity of maintenance required to maintain a desired level of performance and efficiency. Increased attention to mass balance, numerical goals, total maximum daily loads (TMDLs), and non-degradation requirements has created the need for more emphasis on stormwater BMP operation and maintenance (O&M) in order to meet permitting and reporting requirements. The purpose of this paper is to advance knowledge about routine and non-routine maintenance so as to develop more useful O&M plans. To do so, we reviewed literature throughout the United States for maintenance costs and developed, distributed, and analyzed the results of a detailed municipal public works survey. The specific goals of the survey were to identify and inventory O&M efforts and associated costs for stormwater BMPs. Survey questionnaires were sent to 106 cities, 28 of which responded. The survey related to the following topics: number of stormwater BMPs in the city, frequency of inspections and maintenance, average staff-hours spent per routine inspection or maintenance, complexity of maintenance, most frequent causes of performance deterioration, and cost of non-routine maintenance activities. The results of the survey revealed that most (89) cities perform routine maintenance once per year or less. The most common causes of performance deterioration and the greatest expense were sediment buildup and litter/debris for most stormwater BMPs. The nationwide literature review resulted in predictive equations for O&M cost of stormwater BMPs as a function of total construction cost. A general rule of thumb is provided for estimating the relative importance of O&M in life-cycle costs.