l-glutamine was approved by the U.S. Food and Drug Administration (FDA) for sickle cell disease (SCD) in 2017. A vaso-occlusive crisis (VOC) occurs in persons with SCD and is associated with acute pain episodes. This systematic review summarizes the evidence for l-glutamine in the prevention of VOC and associated pain in patients with SCD. Medline, Embase, and International Pharmaceutical Abstracts were searched for records reporting on l-glutamine use in persons with SCD. Eligibility criteria identified primary reports of investigations conducted in humans who were administered l-glutamine, reported on outcomes related to VOC or associated pain, published in English, and were available as full text. All relevant efficacy, safety, participant demographic data, and study method characteristics were extracted and documented. Risk-of-bias assessments were conducted using the Risk of Bias in Non-Randomized Studies-of Interventions (ROBINS-I) tool and the revised Cochrane risk-of-bias tool for randomized studies. Three studies assessing the effect of exogenous l-glutamine administration in patients with SCD met eligibility criteria: one prospective nonrandomized controlled study and two prospective randomized controlled trials. Rate of VOC and related hospitalizations were reduced in patients receiving l-glutamine, although some conflicting results were noted between studies. l-glutamine was generally well tolerated. Limitations of one or more of the eligible studies included small sample size, nonblinding, and study groups that differed at baseline. l-glutamine has limited high-quality evidence supporting its use. Although l-glutamine is FDA approved for the prevention of frequent episodes of VOC pain, only one randomized controlled trial has strong evidence to support this indication. Based on the results of a systematic review, l-glutamine may be considered for patients unable to receive hydroxyurea or in addition to hydroxyurea for reduction in VOC and associated pain. © 2019 Pharmacotherapy Publications, Inc.