Our objectives were to review all reported cases of late flap failure in head and neck surgery and describe any relevant patterns. We conducted a systematic review of all published cases of free flap failure after postoperative day 7 in head and neck surgery from January 1990 to January 2018. Data were collected with respect to flap type, site of reconstruction, reason for failure, and time to failure. A total of 45 cases of late free flap failure in the head and neck were identified. Among the 34 cases in which the necessary data were available for analysis, 50% of late failures occurred between postoperative day 7 and 14. Common reasons for failure were abscess and vascular compromise. We conclude that most late flap failures occur in the second postoperative week. In patients with risk factors for flap failure, close monitoring for up to 14 days after surgery could detect flap compromise before the flap is lost.