This study examines the influence of thermal overlap effects on the ultrasonic attenuation of polydisperse emulsions. The ultrasonic attenuation coefficient of a series of corn oil-in-water emulsions was measured as a function of droplet concentration (1-50 wt %), volume-surface mean droplet radius (r(32) = 0-12 and 0.58 mu m), and frequency (1-120 MHz). There was good agreement between these measurements and predictions of the traditional ultrasonic scattering theory (UST) for the emulsions containing 0.58 mu m droplets, but the UST greatly overestimated the attenuation of the emulsions containing 0.12 mu m droplets, especially at higher droplet concentrations, due to thermal overlap effects. We show that the UST can be extended to account for these effects using a core-shell model and highlight the range of experimental conditions over which the existing UST can be successfully used.