The research literature describes a positive relationship between seeing plants and human well-being. More rapid recovery from surgery, reduced incidence of neighborhood crime, increased baby birth weight and increased trust of neighborhood merchants are some of the outcomes attributed to exposure to trees and shrubs. In this project we attempted to find a common explanation for these outcomes. We examined the connection between urban trees and community stress. Each of the above outcomes can be attributed, in part, to stress reduction. The health literature indicates that stress reduction is one of the consequences of exposure to plants in controlled settings. We wanted to see if exposure to city trees would have the same impact on residents. Stress levels were measured at the block level in Wilmington, Delaware, by means of a survey mailed to 1982 residents. Physical conditions were catalogued using an on-site inventory. The survey and inventory demonstrated that the total number of trees on a block has a strong negative relationship with community stress and a positive relationship with self-reported health. The results suggest that moderation of stress is one of the factors that underlies the beneficial consequences of exposure to green vegetation on inner city blocks. With this information we come one step closer to quantifying the psychological impact of city trees on human behavior.