In children and adolescents with myelomeningocele (MMC), the relation between muscle mass and body composition varies considerably which makes it difficult to evaluate the relevance of renal function assessments with serum(s)-creatinine. Therefore, a reference-interval for enzymatic s-creatinine in individuals with myelomeningocele was constructed.Patients with MMC aged 1.5 to 18 years who consistently had had Cr51 edetic acid clearance within normal limits (88 to 132 ml/min/1.73 m2) were selected for the study. Included were 52 girls and 71 boys with a total of 471 s-creatinine determinations. Children with normal body composition were used as controls.The mean enzymatic s-creatinine concentration at the age of 1.5 years was 22 μmol/L in girls and 21 in boys and increased to 38 μmol/L in girls and 58 in boys at the age of 18 years. There was no difference between the genders until the age of 12. From the age of 3 years, there was a significantly lower median s-creatinine concentration in the MMC children compared to a healthy age-matched population. In fact, the median concentration of the MMC children was equivalent to the 2.5 percentile of the control group.From the age of 3 years, the reference-interval for children and adolescents with MMC showed a lower median concentration for enzymatic s-creatinine and a greater inter-individual variation compared to the healthy age-matched population.