Trunk control is essential for the performance of everyday tasks. Children with neurological impairments such as cerebral palsy (CP) or acquired brain injury (ABI) commonly show impaired trunk control, which leads to restriction in functional activities. The aim of this study was to provide construct validity of the German version of the Trunk Control Measurement Scale (TCMS). We investigated convergent and discriminant construct validity by comparing the TCMS with the Gross Motor Function Classification System (GMFCS) and the modified Timed up and Go (mTUG). Several TCMS items were validated with force plate measurements. The centre of pressure (COP) parameters included the standard deviation of amplitude, the COP displacement and the area. Fifty-two children with CP and ten children with ABI (mean age 10.9 years 4.9 months, range 5-18 years, GMFCS levels I-IV) participated. Spearman rank correlation coefficients calculated between the TCMS and the GMFCS and mTUG amounted to -0.75 and -0.42, respectively. Validating TCMS items with COP parameters was difficult. Nevertheless, the results support the validity of the TCMS in children with brain lesions. This study provides paediatric therapists working in German speaking countries with a valid tool to assess impaired trunk control in these children. Although originally designed for children with CP, our results show that the TCMS may also be applicable to children with ABI, but more research is needed on a larger population.