Fields that experience wet weather after N fertilizer is applied may lose N and consequently lose yield. Replacing N may be difficult or expensive after corn is too tall for tractor clearance. A tool to assess the degree of potential yield loss would help corn producers decide how much expense is justified in making late N applications. Our objective is to develop a general relationship between aerial photo color and yield loss that could be applied to an unknown field to predict yield loss due to N deficiency. Five production corn fields were selected in 2001, a year with a wet spring and visual N deficiency symptoms in many corn fields. All fields had uniform fertilizer history. The rectified aerial photo was broken into polygons corresponding to each yield monitor point. Reference green and reference yield values were based on the darkest 20% of polygons. Relative green (observed green/reference green) and relative yield were calculated for each polygon. Polygons were divided into color classes with equal class interval. Average relative green, relative yield, and yield loss were calculated for each color class. Regression was used to relate relative yield and yield loss to relative green value in the photos. Relative green was a highly significant predictor of relative yield and of yield loss in each field, with R2 values ranging from 0.62 to 0.92. When results were combined across the five fields, relative green was a highly significant predictor of relative yield (R2 = 0.64; P = <.0001) and yield loss (R2 = 0.66 ; P = <.0001). Use of aerial photos appears promising to predict yield loss due to N deficiency in wet years and to inform management decisions about supplemental N.