With funding from the Climate Observations and Services Program, the National Climatic Data Center supports the development of climate indices that measure the impacts of climate and climate variability on sectors of the United States economy and society. This paper describes the development of indices for monitoring of weather and climate conditions associated with the incidence and spread of vector-borne diseases. Disease vectors have climatic thresholds that govern their abundance and their potential for transmitting disease. Though weather fluctuations and seasonal-to-interannual climatic variability influence many disease vectors, this information is not always employed in vector control activities. There are two primary reasons for this disconnect between climatic information and vector management. First, complex relationships between climate and vectors of infectious disease are highly dependent upon local-scale parameters. Second, interaction between climatologists and entomologists has not always been at the level where information can be readily employed in vector management schemes. We have initiated working interactions with entomologists and mosquito control agencies in three pilot areas: Illinois, New York, and South Carolina. We have acquired and organized mosquito surveillance data, compiled climate data and synchronized with mosquito data, and analyzed temporal and spatial patterns of mosquito abundance. We are experimenting with indices such as degree-day thresholds, first and last frost dates, and moisture surplus for development of an early-warning system. Decision-makers may use these indices to identify areas at high risk for disease outbreaks. Subsequent decision-maker actions, such as vector control or medical pre-positioning, may then inhibit or in the most ideal circumstance prevent disease outbreaks. Disease early-warning systems could be based on a complement of antecedent and ongoing climatic conditions, ecological indicators, and epidemiological surveillance systems.