Background/objectives: Glucose Transporter 1 Deficiency Syndrome (GLUT1-DS; OMIM #606777) is a rare disease caused by dominant mutations in SLC2A1 encoding GLUT1, which is a ubiquitous transporter of glucose across plasma membranes, particularly across the blood-brain barrier. Hypoglycorrhachia symptoms are the cornerstones of GLUT1-DS, but delayed growth has also been suggested. This led us to investigate, at diagnosis, the relationship between the glycemia/glycorrhachia ratio and the nutritional and growth pattern phenotype of 30 GLUT-DS patients. Subjects/methods: An assessment was made of body weight (BW), body length/height (BL, BH) and body composition by anthropometry and DEXA, and the results put with BL and BW at birth, genetic target, glycemia, insulinemia, and glycorrhachia values. Results: At birth, 21% of patients had a BW below −1.645 z-score, whereas no patients had BL below the reference values. At diagnosis 23% of the patients had an impaired nutritional status, 19.2% and 3.8% being respectively underweight and overweight/obese; 10%, all under 10 years old, had BL/BH below −1.645 z-score, with no specific features related to body composition. Finally, there was no association between glycemia, glycorrhachia, and growth phenotype. Conclusions: GLUT1-DS is associated with impaired BW but not BL intrauterine growth, with a slower than normal pattern of growth rather than growth failure. These data could be useful for the interpretation of any long-term effects of the ketogenic diet, e.g. nutritional and growth pattern decline.