OBJECTIVE : Children with cerebral palsy (CP) are at risk for under-nutrition. The European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) guidelines identified anthropometric nutritional red flags for neurologically impaired children: weight for age z-score (WFA) < -2, triceps skinfold (TSF) or arm muscle area (AMA) < 10th centile and faltering weight. This study aimed to (1) evaluate the nutritional status of Flemish children and adolescents with CP using different anthropometric indicators; (2) assess the prevalence of nutritional red flags and (3) identify risk factors for low anthropometric parameters. METHODS : This study was a prospective, longitudinal observational study recruiting children and adolescents with CP (2-20 years) in 9 specialized Flemish centres. Measurements were performed at baseline (t1, n = 325), after 6 (t2, total n = 268) and 12 months (t3, total n = 191). WFA z-scores were based on Flemish growth charts; TSF, subscapular skinfolds (SSF) and AMA compared with US reference data. Weight faltering was defined as ≥0.5 decrease in weight SDS at t2 or t3. RESULTS : At t1 50 patients (15.4%) were classified as gross motor function classification system (GMFCS) 1, 95 (29.2%) as GMFCS 2, 49 (15.1%) as GMFCS 3, 54 (16.6%) as GMFCS 4, and 77 (23.7%) as GMFCS 5. The overall median (Q1; Q3) age was 11.7 (8.2; 15.9) years; 61.5% were boys and 22 (6.8%) had a gastrostomy (17 (22.1%) of GMFCS 5 group). The median (Q1; Q3) WFA z-score was -1.13 (-2.6; -0.1); 71.4% of the GMFCS 5 children had a WFA z-score < -2. The median (Q1; Q3) MUAC z-score was 0.17 (-0.7; 1.0); 16.9% of the GFMCS 5 children had MUAC z-score < -2. Median (Q1; Q3) TSF and SSF z-scores were respectively -0.01 (-0.8; 0.9) and 0.27 (-0.3; 0.9). All anthropometric indices tended to decrease with increasing GMFCS (p < 0.001). At t1 42.1% had at least one nutritional red flag, at t2 40.3% and at t3 41.4%. Of those with at least one nutritional red flag at t1 or t2, respectively 14.7% and 18.8% suffered weight loss 6 months later. A GMFCS >2 and dysphagia were associated with a higher risk for lower scores of nearly all nutritional indices. CONCLUSIONS : Underweight was detected in almost three quarters of CP patients with GMFCS 5 classification, whereas deficits in subcutaneous fat and arm muscle reserve were observed in one fifth. Nutritional red flags, present in about 40% of the Flemish CP children, were apparently not successfully addressed in clinical practice, since up to one-fifth of CP patients with warning signs lost even further weight in the following 6 months. Beside a GMFCS >2, dysphagia was one of the most common conditions influencing the presence of low nutritional indices.