A combined simplex/air-assist atomizer with swirl is characterized in an isothermal high pressure spray characterization chamber, with optical access, under various ambient pressures. A single-component, phase Doppler laser interferometer is used to obtain spatially resolved droplet size and velocity information. Data are obtained at atmospheric pressure as well as 3 and 6 atmospheres for conditions of constant fuel and atomizing air flow rates. Two different nozzle air flow rates and, hence, two different air-to-liquid ratios are considered. The appropriate scaling parameters for the extrapolation of atmospheric testing data to high ambient pressures are likely geometry specific, and will require data of the type reported here.