BACKGROUND: Flexor tendon repairs using conventional suture require knots that enlarge the cross-sectional area at the repair site. This enlargement increases the force of finger flexion and jeopardizes the integrity of a nascent tendon repair during rehabilitation. The authors hypothesized that a knotless flexor tendon repair using bidirectional barbed suture has similar strength and with reduced cross-sectional area compared with traditional techniques. METHODS: Sixty-six fresh porcine flexor digitorum profundus tendons were divided randomly into three groups. Tendons were transected and repaired with one of the following techniques: two-strand Kessler technique, four-strand Savage technique, or four-strand knotless technique. The cross-sectional area of each tendon was calculated at the repair site before and after repair. All tendons underwent mechanical testing to assess the 2-mm-gap formation force and ultimate strength. RESULTS: The 2-mm-gap formation force and ultimate strength of the Savage and knotless technique groups were not significantly different; however, both were significantly greater than those of the Kessler repair group (p<0.05). The repair-site cross-sectional area of tendons repaired with the knotless technique was significantly smaller than that of tendons repaired with the Kessler or Savage technique (p<0.01). Tendons repaired with the knotless technique also had a significantly smaller change in repair-site cross-sectional area (p<0.01). CONCLUSIONS: The authors demonstrate that knotless flexor tendon repair with barbed suture has equivalent strength and reduced repair-site cross-sectional area compared with traditional techniques. The smaller tendon profile may decrease gliding resistance, thus reducing the risk for postsurgical tendon rupture during rehabilitation.