Splints with or without wrist immobilization can be used during the rehabilitation of flexor tendon lesions of the hand. The evidence base for these techniques has not previously been studied in a systematic review. We sought to thoroughly review patient-reported functional outcomes and pain to compare splinting with or without wrist immobilization. Five bibliographic databases were searched. Studies were considered for inclusion if they were randomized controlled trials or observational comparative studies reporting the difference in outcome among patients treated with or without wrist immobilization. No limits were set on publication date or language. Study selection was performed independently by two authors, and disagreements were resolved by consensus. The review protocol was preregistered in PROSPERO. There were no randomized controlled trials. No studies could be included based on our inclusion criteria. We decided to qualitatively summarize the most relevant studies although they did not meet our inclusion criteria. This resulted in a narrative review of the studies we found relevant. Based on the current literature, it is impossible to provide evidence-based recommendations for or against wrist immobilization during the rehabilitation period following flexor tendon repair. The lack of high-quality evidence points to a need for randomized clinical trials to guide rehabilitation decisions.