Response to mid-day wilting (dehydration avoidance) among sweet potato [Ipomoea batatas L. (Lam)] genotypes is a consistent trait within and among years. This response is significantly related to storage root dry weight and net photosynthesis in most years. The relationship is more obvious among relatively high-yielding clones or when data are obtained over several years. Reduced mid-day wilting increases yield in high-yielding genotypes through increased net photosynthesis and increased partitioning of assimilates to storage roots. Increased storage root dry weight is also related to the percentage of water in the vines at near full-turgor through increased partitioning to roots and reduced mid-day wilting. Wilting response and vine moisture together account for nearly 25% of the variation in yield of high-yielding clones tested over 5 years with irrigation.