OBJECTIVE Recent reports have described severe precocious pulmonary emphysema in persons who inject methylphenidate (crushed Ritalin tablets) i.v. We retrospectively evaluated the plain radiographic and CT features in 21 such patients. METHODS The chest radiographs, available CT scans, and clinical and pathologic data were reviewed in 21 cases of i.v. Ritalin use. The patients were from 35 to 54 years old. Twelve patients were men, and nine were women. Emphysema was graded on the basis of findings on chest radiographs, by consensus, on a four-point scale as absent, mild, moderate, or severe. CT scans were available for three patients, including one imaged after a single lung transplantation. Autopsy results were available for four patients. Fixed inflated lung specimens and corresponding high-resolution CT scans were available in three cases. RESULTS Radiographs showed pulmonary emphysema in all cases. The distribution of disease was basilar and symmetric. Small apical bullae were suggested in only one case. Basilar emphysema was rated as mild in four patients, moderate in three patients, and severe in 14 patients. In 11 patients who had serial chest radiographs, the basilar emphysema was noted to progress over a 2- to 7-year period. No evidence of progressive massive fibrosis was seen in any patient. CT scans confirmed emphysema, most severe at the lung bases. CONCLUSIONS The plain radiographic and CT findings in patients who inject Ritalin are similar to those found in patients with alpha 1-antitrypsin deficiency and different from the findings seen in other types of i.v. drug use. The finding of basilar pulmonary emphysema should alert the radiologist to the possibility of i.v. injection of Ritalin.