PURPOSE: To demonstrate the histopathologic characteristics of different types of lacrimal drainage system concretions with clinical correlations. METHODS: Thirty lacrimal drainage system concretions submitted to the Cogan Eye Pathology Laboratory at the Massachusetts Eye and Ear Infirmary over a 2-year period were reviewed. Concretions were studied in detail using their histopathologic staining features as revealed with hematoxylin and eosin, Gomori methenamine silver, periodic acid-Schiff, iron stain, and Brown-Hopps tissue gram stain. A separate retrospective chart review was conducted for each patient to identify any clinical correlations. RESULTS: Two major forms of concretions were identified histopathologically: mucopeptide (7) and bacterial (20). Mucopeptide concretions were found exclusively within the lacrimal sac, while bacterial concretions were found chiefly in the canaliculus. A third category of "mixed" concretions with substantial mucopeptide and bacterial characteristics comprised 3 specimens. Bacterial concretions consisted of large matted masses of filamentous, presumed Actinomyces organisms that were easily identified with the Grocott's methenamine silver stain; they were frequently cocolonized at their edges with coccal bacterial forms. Mucopeptide concretions were generally devoid of cellular elements and were composed of broad bland whorls of diffusely eosinophilic, acellular, periodic acid-Schiff-positive material punctuated by lacunae. They were often cocolonized by small numbers of bacterial cocci and occasional fungi. Culture results disclosed low virulence species. All 3 types of concretions predominated in women. Patients with bacterial concretions frequently had dry eye symptoms. CONCLUSIONS: The 2 major types of lacrimal system concretions differ in their primary location and histopathologic composition. Further characterization may lead to an understanding of the mechanisms for their formation. Mucopeptide concretion is more appropriate than terms such as "dacryolith" and "mucolith," and bacterial concretion is a more appropriate term than "canaliculith," because of the absence of significant calcium or stone-like density in these masses.