In 2012, 543 harbor seals (Phoca vitulina) and 124 grey seals (Halichoerus grypus) were admitted to the Seal Rehabilitation and Research Centre in Pieterburen, The Netherlands. In 19 seals (3%), signs of infection in a hind flipper were observed. Initial treatment consisting of antibiotics and anti-inflammatory drugs resolved the symptoms in 15 animals. In four harbor seals, estimated to be 3 to 4 mo old, a necrotizing infection developed that resulted in osteoarthritis of the tarsus or tibiotarsal joint or both. Bacterial culture revealed the presence of polymicrobial infection in three of the four animals. Treatment consisted of amputation of the hind flipper under general anesthesia combined with tumescent anesthesia in the operation field. Amputations were done at the diaphysis of the tibia and fibula. After resecting these bones, the flipper was discarded, leaving a good muscle-skin cuff to cover the edges of the bones and close the skin without tension. The estimated blood loss varied between <50 to 150 ml. Healing was uneventful, and both antibiotics and analgesics were gradually reduced according to the individual response. The seals did not show any functional impairment 1 mo postoperatively. After release to the sea, scrutinous revision of all radiographs showed signs of osteomyelitis in at least one animal in the proximal part of the tibia, also present preoperatively. It is concluded that tumescent anesthesia in seals may reduce perioperative blood loss and that a lower leg amputation is a surgically easy and clean approach for the treatment of osteoarthritis of the hind flipper of seals, giving good functional results (diving, catching fish, exiting a pool, and moving on land).