A 5-year-old male castrated Lhasa Apso cross was evaluated for a 1-month history of inappetence, lethargy, gagging, and progressive right thoracic limb lameness. Synovial fluid analysis revealed nonseptic suppurative inflammation, and a diagnosis of immune-mediated polyarthritis (IMPA) was made. After 3 months of treatment with prednisone and later cyclosporine, the dog developed multiple firm cutaneous and subcutaneous masses and a focal mass within the jejunum. Cultures of blood, urine, skin lesions, and the jejunal mass identified Nocardia veterana by matrix-absorption laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and allowed for earlier identification of the organism compared to more traditional secA1 gene sequencing. Immunosuppressive drug treatment was discontinued, and the dog was treated for 3 months by administration of trimethoprim-sulfamethoxazole (TMS). No recurrence of clinical signs was reported 1 year later. This case report highlights the clinical utility of MALDI-TOF MS, particularly for the rapid identification of slow-growing, fastidious organisms.