BACKGROUND: Biallelic pathogenic variants in PGM1 result in phosphoglucomutase 1 (PGM1) deficiency that is one of the congenital disorders of glycosylation (CDG) (PGM1-CDG). Phenotypic spectrum includes congenital malformations, and muscular, cardiac, hepatic, endocrine and hematologic phenotypes. Current treatment consists of D-galactose therapy that results in clinical and biochemical improvements. To improve fatigue, and exercise intolerance, we started creatine supplementation therapy. MATERIAL AND METHODS: We reviewed electronic patient chart. We applied Nijmegen Pediatric CDG Rating Scale (NPCRS) and The Functional Assessment of Chronic Illness Therapy Fatigue scale (FACIT-F). We measured creatine metabolism biomarkers. RESULTS: This is a 29-year-old female with PGM1-CDG, confirmed diagnosis by clinical exome sequencing. She has been treated with D-galactose therapy which did not improve her fatigue and exercise intolerance. She was started on creatine supplementation therapy at the age of 27 years which led to decreased daytime sleeping, increased exercise capacity and improvements in her NPCRS, and FACIT-F. Her plasma guanidinoacetate was low. She had elevated urine galactitol on D-galactose therapy. DISCUSSION: PGM1-CDG associated myopathy is likely due to combination of several factors including abnormal muscle carbohydrate metabolism, abnormal N-glycosylation of proteins involved in the muscle functions and creatine transport and altered muscle energy homeostasis. It was previously shown that creatine supplementation therapy improves myopathy in patients with mitochondrial cytopathies. We think that the use of creatine supplementation therapy coincided with improvements in fatigue and exercise intolerance subjectively and objectively in our patient.