MIT Lincoln Laboratory is being sponsored by the Federal Aviation Administration (FAA) to develop and test the Terminal Doppler Weather Radar (TDWR) wind shear surveillance system. As part of this program Lincoln has developed algorithms for automatically detecting microbursts, or thunderstorm outflows using the radial velocity data gathered from a single TDWR. Output from the detection algorithms will be used to warn aircraft of microburst hazards. While the success in automatically detecting microbursts using the Lincoln Laboratory microburst detection algorithm has been encouraging, one issue which continues to cause concern is microburst asymmetry. Asymmetry, or aspect angle dependence, in microbursts refers to outflows that have a divergent surface outflow strength or extent what varies depending on the aspect (or viewing) angle of the radar. The TDWR detection algorithms utilize input from a single Doppler radar; therefore, an asymmetric microburst may be underestimated or go undetected if the radar is viewing the event from an aspect angle where the strength of the outflow is weak. Additionally, the size and location of the event may be distorted when the outflow extent is significantly asymmetric. Most of the present outflow modeling and detection methods are based on the assumption of axial symmetry both in the strength and extent of outflows. Asymmetry in microbursts, therefore, is a major concern for TDWR microburst detection performance. Past work by Wilson et al. and Eilts has indicated that some microbursts are highly asymmetric, for at least a portion of their lifetime. However, this previous work has been limited in scope to single "snap-shots" of the microbursts, generally at their peak outflow strength. Strength asymmetries from these previous studies indicated asymmetry ratios (maximum over minimum strength) ranging from 1.3:1 to as high as 6:1. None of the studies dealt with shape (or extent) asymmetries. This paper describes the results from a detailed study of 96 individual observations from 27 microburst events. Measurements were taken to determine both the strength and extent of each microburst at multiple aspect angles. The data clearly show that microbursts, on average, have maximum strengths and extents which are 1.9:1 and 1.5:1 asymmetric, respectively.