Congenital disorders of glycosylation (CDG) are a group of metabolic disorders caused by deficient protein glycosylation. PMM2-CDG, the most common CDG, is caused by phosphomannomutase (PMM) deficiency. Clinical symptoms often include neurological involvement in addition to dysmorphic features, failure to thrive, cardiac failure, renal, and endocrine abnormalities. To our knowledge, lymphatic edema in CDG has not been reported. We present two cases of lymphatic edema in PMM2-CDG patients. The first patient was noted to have a larger right leg circumference at two years. Ultrasound investigations did not reveal any obvious vascular or lymphatic malformation. The swelling increased in size over time. At 12 years, lymphoscintigraphy revealed decreased lymphatic draining in both legs, which was more profound in the right leg. The second patient was treated for pulmonary stenosis at age 2 months. Postoperative, the patient suffered from protein-losing enteropathy, hypothyroidism, recurrent bacterial infections, and bilateral lymphatic edema. General condition improved after thyroxin treatment and albumin infusions; however, the bilateral pedal and leg edema remained unresolved. Contrast studies of the lymphatic system showed bilateral hypoplasia distal to the knees. Although both children had secondary factors worsening lymphatic edema in PMM2-CDG, hypoalbuminemia, recurrent infections, cardiac failure, and endocrine abnormalities could not fully explain the clinical features. The additional factors were treated successfully but the therapy did not resolve the lymphatic edema. Based on the abnormal imaging studies of the lymphatic system, we propose that lymphatic vessel hypoplasia is the major cause for lymphatic edema in our patients with PMM2-CDG.