A 7-year-old castrated male Miniature Schnauzer was examined because of labored breathing and episodes of respiratory distress that progressed to collapse. On cervical radiographs, a focal soft tissue mass in the caudal cervical portion of the trachea was observed, and during tracheoscopy, a 1 x 1 cm, pedunculated, multinodular, pink, intraluminal mass extending from the dorsal tracheal membrane and obstructing approximately 80% of the tracheal lumen was seen. Tracheal resection and anastomosis was performed to remove the mass, and the dog recovered without complications. On histologic examination, the mass consisted of a large accumulation of homogeneous, faintly fibrillar eosinophilic material admixed with a predominantly plasma cell infiltrate; examination of sections stained with thioflavin T and Congo red stain confirmed that the eosinophilic material was amyloid. A diagnosis of nodular, immunocyte-derived (AL) amyloidosis was made. Seventeen months after surgery, the dog had a relapse of respiratory distress because of an extramedullary plasmacytoma involving the trachea.