Abstract Objective The objective of this study was to assess the prevalence of elevated insulin-like growth factor (IGF)-1 in children with suprasellar low-grade glioma (LGG) and explore the course of IGF-1 over time and its association with anthropometrics, hypothalamic syndrome, tumour characteristics, and tumour behaviour. Design This retrospective study included children from the Netherlands and the United Kingdom diagnosed with a suprasellar LGG under the age of 18 between 2003 and 2023, with a minimum 1-year follow-up. Elevated IGF-1 was defined as IGF-1 standard deviation score (SDS) >+2.0 for age and biological sex, without growth hormone use. Results We included 235 patients with a median age at brain tumour diagnosis of 3.8 years (IQR 1.7-7.1). Elevated IGF-1 was observed in 73 patients (31.1%) at any time point. At tumour diagnosis, 15.2% of the 138 children tested showed elevated IGF-1. Elevated IGF-1 was associated with younger age at tumour diagnosis (P = .004), neurofibromatosis type 1 (NF1; P = .028), and diencephalic syndrome (P = .047). In 55 of the 73 patients with elevated IGF-1 (75.3%), IGF-1 normalized spontaneously over time. Final height SDS corrected for target height SDS was not associated with having had an elevated IGF-1 (P = .113). No difference was found in the number of tumour progressions. Conclusions Increased IGF-1 concentrations are commonly observed in children with suprasellar LGG, especially in younger children, those with an NF1 mutation, or during underweight. Elevation of IGF-1 can resolve over time, and the absence of an effect on final height or on tumour progressions seems reassuring.