Objective: To determine the efficacy of oral extended-release hydrocodone compared with oral firocoxib for analgesia following tibial plateau leveling osteotomy surgery in dogs in a hospital setting. Study design: Prospective, randomized, blinded, clinical trial. Animals: Thirty-six client-owned dogs weighing 25-43 kg with unilateral hindlimb lameness and cranial cruciate ligament rupture. Methods: Dogs were assigned to 1 of 2 groups (n = 18/group). Group 1 received hydrocodone 3 mg/kg orally every 24 hours, and group 2 received firocoxib 5 mg/kg orally every 24 hours. Both hydrocodone and firocoxib (according to group assignment) were provided as preemptive analgesia 10 hours before induction to anesthesia and then every 24 hours for the remainder of the study period The level of analgesia was compared between treatments on the basis of a modified Glasgow Composite Pain Score (mGCPS) in each dog, the number of dogs requiring rescue analgesia (hydromorphone 0.05 mg/kg subcutaneously), pressure platform stance data, and number of adverse events. Results: Nine of 18 dogs that received hydrocodone and 2/18 dogs that received firocoxib had an mGCPS ≥6 (P =.02). Two dogs had an mGCPS ≥6 three times, and 1 had an mGCPS ≥6 two times; all 3 of these dogs were in the hydrocodone group. Average postoperative peak pressure placed on the affected limb was lower in dogs that received hydrocodone (P =.01). Regurgitation and decreased appetite were more common in the dogs that received hydrocodone. Conclusion: Dogs that were treated with hydrocodone exhibited higher pain scores and lower limb function than dogs treated with firocoxib under the conditions of our study. Clinical significance: Our results do not provide evidence to justify the administration of extended-release hydrocodone at 3 mg/kg orally every 24 hours rather than firocoxib at 5 mg/kg orally every 24 hours in dogs undergoing tibial plateau leveling osteotomy.