A 6-year-old, 43-kg, spayed female rottweiler was presented for a 1-month history of progressive, left hind-limb lameness. Upon physical examination, a cranial drawer sign and joint distention were present in the left stifle. Radiographically, the stifle had evidence of effusion, remodeling of the patella, and an enlarged popliteal lymph node. Marked synovial thickening and an intact cranial cruciate ligament were noted during surgery. Despite finding a nonspecific, mixed inflammatory response on joint fluid cytopathology, histopathology demonstrated T-cell lymphoma of the synovium. Lameness may be the sole presenting clinical sign in canine lymphoma.