Crospovidone is an insoluble polymer of N-vinyl-2-pyrrolidone that is used as a disintegrant in pharmaceutical tablets. It can potentially embolize to the lung when aqueous tablet suspensions are injected intravenously. In this report, we identified embolized crospovidone in autopsy-derived lung tissue from three adult IV drug users, 1 man and 2 women, whose ages respectively were 27, 38, and 40 years. Suspected crospovidone was compared with pharmaceutical-grade crospovidone by means of histochemical stains, transmission electron microscopy, and infrared spectroscopy. Similar particles were also observed by light microscopy in a 4-mg tablet of hydromorphone, a preparation prescribed to two of the patients. Two patients had sickle cell disease and were taking methadone and/or hydromorphone for pain management; the third was receiving parenteral hyperalimentation after small bowel resection. Crospovidone appeared as deeply basophilic, coral-like particles within pulmonary arteries and in extravascular foreign-body granulomas. Intrapulmonary crospovidone stained similarly to the pure substance, including intense staining with mucicarmine, Congo red, and Masson trichrome. With Movat pentachrome stain, both intravascular and purified crospovidone appeared orange-yellow, whereas most interstitial particles associated with giant cells stained blue-green. Alcian blue failed to stain intravascular or purified crospovidone but strongly decorated some phagocytized particles. Ultrastructurally, both purified powder and tissue deposits of crospovidone appeared as irregular, electron dense, laminated, and finely granular material. Intrapulmonary crospovidone was associated with inflammatory cells and exhibited degenerative changes. By infrared spectroscopy, crospovidone in tissue had the same spectral characteristics as pharmaceutical grade crospovidone and the library reference, polyvinylpyrrolidone (PVP). We conclude that crospovidone contributes to pulmonary vascular injury in some persons who illicitly inject pharmaceutical tablets. It is readily identifiable histologically and distinguishable from other tablet constituents, such as cornstarch, talc, and microcrystalline cellulose. The variable staining with Alcian blue and Movat suggests that crospovidone is altered in vivo by the inflammatory response.