Pain is a subjective, aversive sensory and emotional experience and can cause or exacerbate problem behaviors. In this review, the biobehavioral model of pain is introduced and used to improve understanding by veterinarians of pain mechanisms and their relationship with problem behaviors. A range of potential indicators of discomfort are presented, illustrated by selected cases from the authors’ behavior and pain referral clinics. Various myths exist around pain resulting in barriers to reporting assessment and treatment. Veterinarians should always consider discomfort in any case presenting with a problem behavior.