The dimensional stability of V-shaped composite parts made from polyamide-12/carbon fibre (PA12/CF) commingled yarn has been studied. An anisotropic, thermoviscoelastic material model was implemented in a finite element solver to predict the internal stresses induced during the processing of the composite. Excellent correlation was found between predicted and experimentally measured stress profiles for compression-moulded parts. The stresses were related to the dimensional stability of the parts after demoulding and the effect of key processing parameters on dimensional stability was investigated.