Congenital Disorders of Glycosylation (CDG) are a group of some 200 genetic disorders with PMM2-CDG being the most common disease. These disorders individually remain rare with poorly understood natural history (NH) and causes of mortality. We established a NH study for CDG and collected both prospective and retrospective data on CDG outcomes. In the current data set analysis on deceased patients, we describe the clinical phenotype and causes of death for thirty-seven individuals with various genetic causes of CDG. About a third of this cohort were affected with PMM2-CDG. All of the patients presented with multisystem features with involvement of the neurological system. The majority of patients involved in this study died during the first three years of life, and only four patients lived beyond ten years. The cause of death was unavailable for two patients, and about a third died secondary to cardiopulmonary failure. Progression of neurological involvement, sepsis and respiratory infection were also among the reported causes. Pericardial effusion was the primary cause of death for three infants affected with PMM2-CDG. This study emphasizes the importance of diagnosis and supportive care following the published monitoring and management guidelines for affected patients with CDG to optimize their health and development in the early stages of the disease.