The effectiveness of pirfenidone ointment against thermoplasty-induced acute foreleg lameness in a double-blind study, and against acute and chronic lameness of musculoskeletal origin in an open multi-centered field trial was evaluated in this study. Thermoplasty was performed on both inner forelegs at designated locations of each horse under anesthetics. A 10% pirfenidone or placebo ointment was topically applied starting 24 hours after the thermoplasty three times daily for 7 days. For acute and chronic lameness of musculoskeletal origin, pirfenidone ointment was also applied one to three times daily for 7 to 10 days and continued for an additional 20 to 30 days. A marked swelling around the locations occurred in 24 hours post-thermoplasty. The topical application of pirfenidone ointment not only caused a significant reduction in the circumference measurements at 5, 6 and 7 days, but it also decreased the changes in the circumferences from pre-thermoplasty as an index of edema, at 3, 4, 5, 6, and 7 days when compared to the placebo ointment at the corresponding times. Although treatment for 7 days of acute leg lameness of musculoskeletal origin with topical pirfenidone ointment caused significant decreases in swelling, heat, and pain, and improved the degree of flexion when compared with the pretreatment, it had little effect on chronic lameness except that it improved the flexion at the second-exam interval. It was concluded that topical application of pirfenidone is effective for treatment of acute lameness resulting from thermoplasty or from various types of musculoskeletal disorders, suggesting that pirfenidone offers a promising therapeutic potential to manage acute inflammation, an important component of lameness.