The intrasynovial flexor tendon's healing capacity has been a topic of extensive investigations and discussion for several decades. Before 1970, the digital flexor tendon was widely accepted as lacking intrinsic healing capacity. In subsequent decades, however, the intrinsic tendon healing capacity came to light in a series of experimental studies that demonstrated observation of the repair process in lacerated flexor tendons within the synovial sheath, identification of cellular activity and the ability of in vitro tendon cultures to generate matrix. Flexor tendon injuries are open in most cases, resulting from a sharp cut or a crush, but they can also present as closed injuries. Acutely lacerated flexor tendons in the hand and forearm should be treated primarily or at the delayed primary stage whenever possible. The best outcomes of flexor tendon repair came if a skilled surgeon did so within hours. A non-experienced surgeon should not patch the tendon injured in sensitive areas (such as zone 2). The preferred delay period is 4–7 days when the risk of infection can be properly assessed and edema has significantly decreased. Delay of repair after 3–4 weeks can cause myostatic shortening of the muscle tendon unit. In these late cases, tendon lengthening within the forearm muscles may relieve tension. After surgery, rupture of the repaired flexor tendons can be re-repaired if the rupture occurs within a few weeks to a month after surgery. Secondary tendon grafts can be the only option for ruptured cases where there is evident tendon end retraction or significant scarring. A modified Kessler suture can be used instead of the traditional Kessler grasping suture. An advantage of this suture is that the knot is left in the cut surface of the tendon. One possible disadvantage is the difficulty of sliding the tendon on some suture materials to achieve satisfactory approximation of the tendon ends. Modifications described subsequently may minimize the problem of exposed suture material.