ObjectiveThis study identified biomarkers of neurological outcome in Sturge‐Weber syndrome (SWS) via urine angiogenic factors and captured longitudinally derived natural history data within an SWS cohort.MethodsThis longitudinal, prospective, multicentered study of 61 people with SWS aged 0.4–55 years reports port‐wine birthmark score, Neuroscore, Neuro‐Quality of Life, and urine angiogenic factors over a two‐year period.ResultsCognitive Neuroscore worsened over time for children aged 0–2 years. Male sex was associated with worsening Cognitive Function Neuroscore during the study. Age of seizure onset before 2 years was strongly associated with worse Neuroscore. Children with SWS had low Neuro‐Quality of Life related to cognitive function. Seizure severity, male sex, and earlier age of seizure onset were associated with worse Neuro‐Quality of Life in school‐aged children. Children with SWS have elevated basic fibroblast growth factor in their urine compared with controls, whereas higher vascular endothelial growth factor was associated with better Neuroscore.InterpretationThis study is the first multicenter, prospective, and longitudinal study of people with SWS. It identifies significant clinical prognostic factors such as age of seizure onset and male sex, informs symptom progression over time by age group, and suggests that further study of angiogenic mechanisms and potential biomarkers are needed.