Companion animal rehabilitation, a collaborative practice of physical therapy and veterinary medicine, can only demonstrate the effectiveness of its theories, techniques, interventions, and modalities through evidence-based practice, utilizing standardized, reliable, and valid outcome measures, correlated with objective diagnostic data. This essay examines existing and potential objective outcome measures utilized in companion animal rehabilitation and physical therapy regarding pain, vital signs, body condition and composition, range of motion, muscle strength, inflammation, functional mobility, and gait. Discussion is included of the traditional disablement model and the evolution of the physical therapy diagnosis, prognosis, and plan of care.