BACKGROUND: Low-grade gliomas (LGGs) and low-grade glioneuronal tumors (LGGNTs) diagnosed during the first year of life carry unique clinical characteristics and challenges in management. However, data on the treatment burden, outcomes, and morbidities are lacking. METHODS: A retrospective study of LGGs and LGGNTs diagnosed in patients younger than 12 months at St. Jude Children's Research Hospital (1986 was conducted. RESULTS: For the 51 patients (including 31 males), the mean age at diagnosis was 6.47 months (range, 0.17-11.76 months), and the mean follow-up period was 11.8 years (range, 0.21-29.19 years). Tumor locations were hypothalamic/optic pathway (61%), hemispheric (12%), brainstem (12%), cerebellar (8%), and spinal (8%). There were 41 patients with histological diagnoses: 28 had World Health Organization grade 1 tumors, 6 had grade 2 tumors, and 7 had an LGG/LGGNT not definitively graded. Forty-one patients required an active intervention at diagnosis. Throughout their treatment course, 41 patients eventually underwent tumor-directed surgeries (median, 2 surgeries; range, 1-6), 39 received chemotherapy (median, 2 regimens; range, 1-13), and 21 received radiotherapy. Forty patients experienced disease progression (median, 2 progressions; range, 1-18). Ten patients died of progression (n = 5), malignant transformation (n = 2), a second cancer (n = 2), or a shunt infection (n = 1). The 10-year overall survival, progression-free survival, and radiation-free survival rates were 85% ± 5.3%, 16.9% ± 5.3%, and 51.2% ± 7.5%, respectively. Forty-nine patients experienced health deficits (eg, endocrinopathies, obesity, seizures, visual/hearing impairments, neurocognitive impairments, and cerebrovascular disease). Predictors of progression and toxicities were defined. CONCLUSIONS: Infantile LGG/LGGNT is a chronic, progressive disease universally associated with long-term morbidities and requires multidisciplinary intervention.