We report the design and performance of a mammographically configured, dual-sided, automated breast ultrasound (ABUS) 3D imaging system. Dual-sided imaging (superior and inferior) is compared with single-sided imaging to aid decisions on clinical implementation of the more complex, but potentially higher quality dual-sided imaging. Marked improvement in the image quality and coverage of the breast is found in dual-sided ultrasound over single-sided ultrasound. Among hypoechoic masses imaged, there are increases in the mean contrast-to-noise ratio (CNR) of 57% and 79%, respectively, for spliced dual sided vs. superior or inferior single-sided imaging. The fractional breast volume coverage, defined as the percentage volume in the transducer field of view that is imaged with clinically-acceptable quality, is improved from 59% in both superior and inferior single-sided imaging to 89% in dual-sided imaging. Applying acoustic coupling to the breast requires more effort or sophisticated methods in dual-sided imaging than in single-sided.