Annular centrifugal contactors were developed as single, compact units utilized to transfer desired species between immiscible fluid phases. Critical to understanding the mass-transfer characteristics in the annular mixing region is a clear picture of the distribution of droplet sizes of the fluids involved. To date, very little experimental data appears in the literature. We fill that void by using laser fluorescence and optical methods to directly observe and measure drop-size distributions for a silicone oil/water system in a centrifugal contactor. The shape and characteristics of the log-normal distributions, including the Sauter mean diameter and distribution means, are elucidated in terms of rotor speed and organic phase fraction. The size distribution of entrained air bubbles is also examined. The results presented here will be invaluable in validating and expanding the predictive capacity of the many models that have been developed to describe the flow within these devices. Published 2013 American Institute of Chemical Engineers AIChE J, 59: 22192226, 2013