Patient-reported outcomes (PROs) measure important aspects of disease burden, however they have received limited attention in the care of patients with Congenital Disorders of Glycosylation (CDG). We evaluated the PROs and correlation between clinical disease severity scoring and reported quality of life (QoL) in a PMM2-CDG patient cohort. Twenty-five patients with diagnosis of PMM2-CDG were enrolled as part of the Frontiers in Congenital Disorders of Glycosylation Consortium (FCDGC) natural history study. Patient- Reported Outcomes Measurement Information System (PROMIS) was completed by caregivers to assess health-related QoL. Clinical disease severity was scored by medical providers using the Nijmegen Progression CDG Rating Scale (NPCRS). The domains such as physical activity, strength impact, upper extremity, physical mobility, and a satisfaction in social roles (peer relationships) were found to be the most affected in the PMM2-CDG population compared to US general population. We found a strong correlation between NPCRS 1 (current functional ability) and three out of ten PROMIS subscales. NPCRS 2 (laboratory and organ function) and NPCRS 3 (neurological involvement) did not correlate with PROMIS. Mental health domains, such as anxiety, were positively correlated with depressive symptoms (r = 0.76, p = 0.004), fatigue (r = 0.67, p = 0.04). Surprisingly, patients with severely affected physical mobility showed low anxiety scores according to PROMIS (inverse correlation, r = −0.74, p = 0.005). Additionally, there was a positive correlation between upper extremity and physical mobility (r = 0.75, p = 002). Here, we found that PROMIS is an informative additional tool to measure CDG disease burden, which could be used as clinical trial outcome measures. The addition of PROMIS to clinical follow-up could help improve the quality of care for PMM2-CDG by facilitating a holistic approach for clinical decision-making. Synopsis: We recommend PROMIS as an informative tool to measure disease burden in PMM2-CDG in addition to traditional CDG disease severity scores.