A 3-year-old female guinea pig was presented to Hospital Veterinário do Oeste for a 5-cm diameter lump on the neck that had developed over the prior 15 days. An abscessed lymph node was suspected. It was lanced, 45 ml of liquid pus was drained, and samples were sent for cytology and culture/sensitivity. The animal was started on sulfamethoxazole-trimethoprim 20 mg/kg PO BID and meloxicam 1 mg/kg PO SID. Cytology confirmed an abscess. Sphingomonas paucimobilis was isolated from bacterial culture and was sensitive to all antibiotics tested. Twelve days after presentation, affected tissues were much smaller and were surgically resected. Histopathology revealed the lesion was not an abscessed lymph node as had been expected. Instead, it was a subcutaneous abscess that had formed adjacent to salivary gland tissue which was not primarily inflamed. It encompassed muscle fibers, adipose tissue, and dense lymphoid tissue associated with few epithelial inclusions which was reminiscent of thymus. The latter probably represented ectopic thymus and it was considered an incidental finding. Twelve days later the animal was discharged, and antibiotic treatment was stopped. Excision was curative and no local recurrence ever occurred. Sphingomonas paucimobilis is an aerobic gram-negative bacterium found in soil and water. It is a rare cause of healthcare-associated infections, but it has been reported to cause outbreaks of bacteremia among immunocompromised patients in hematology and oncology units. This is the first time Sphingomonas paucimobilis has been described in a guinea pig, and veterinarians and pet owners should be aware of its zoonotic potential.