Silicone lymphadenopathy (SL)--defined as the presence of silicone in a lymph node--is a rare side effect of mammary augmentation either by injection of liquid silicone or by placement of a bag-gel prosthesis. Nine new cases in eight patients are herein reported and compared with six previously well-documented cases. The available data showed that SL was frequently detected as an incidental finding of no clinical significance during mastectomy and nodal dissection for associated breast carcinoma (nine cases), but may present as a painful or nontender enlarged lymph node (six cases). The latter presentation was almost always associated with a history of injection of liquid silicone or rupture of the prosthesis. All or some of the following findings were present in an affected lymph node: coarse vacuoles, fine vacuoles, and multinucleated giant cells. All lymph nodes contained a variable amount of an unstained, nonbirefringent, refractile material that, in seven of our cases, was shown to contain elemental silicon by energy-dispersive x-ray elemental analysis. In 312 lymph nodes collected from 18 routine cases of breast carcinoma, coarse vacuoles probably representing fat were found in 107 lymph nodes (34%); focal fine vacuoles were found in one (0.3%), and a single multinucleated giant cell was found in one (0.3%). In conclusion, SL probably will be encountered more frequently when cancer-prone age is reached by the susceptible population. In most cases, it is an incidental finding of no clinical significance. However, the histologic diagnosis can be made by observing characteristic light-microscopic changes, which may be supplemented in doubtful cases by energy-dispersive x-ray analysis.