The light extinction coefficient, k, for cotton is important due to the increased interest in ultra-narrow cropping systems. The relationship between k, row spacing, and plant density will, in the future, be used in crop simulation models such as EPIC to more accurately predict crop response to various growing conditions. A two-year study was conducted in 1998 and 1999. The objective of this study was to characterize the effect of row spacing and plant density on the extinction coefficient of cotton. A split-plot, randomized complete block design with four replications was used with sixteen treatments consisting of row spacings of 0.15, 0.38, 0.76, and 1.00-m and plant densities of 150, 220, 300, and 450-thousand plants hectare^-1. In 1999 as row spacing increased, k decreased. This was attributed to an increase in LAI with row spacing. Plant density did not influence k, but yield increased as row spacing decreased.