Aim To investigate the relationships between pain in the lower extremities and back, and spasticity, bone/joint complications and mobility. Methods Retrospective population-based registry study. Participants (N = 3256) with cerebral palsy (CP), 2.5-16 years of age, participating in the Swedish Cerebral Palsy Follow-up Program were included. Spasticity was measured using scissoring and the Modified Ashworth Scale. Bone/joint complications consisted of hip displacement, range of motion, windswept posture and scoliosis. Mobility was measured using the Functional Mobility Scale (5-, 50- and 500-metres), wheelchair use (outdoors) and the ability to stand/get up from sitting/use stairs, respectively. Pain was measured as presence of pain in hips, knees, feet and back. Data were analysed using structural equation modelling. Results Bone/joint complications had the strongest direct pathway with pain in the lower extremities (standardised regression coefficient = 0.48), followed by reduced mobility (standardised regression coefficient = -0.24). The pathways between spasticity and pain, and age and pain were not significant. The R-2 of the model was 0.15. Conclusion Bone/joint complications and reduced mobility were associated with pain in the lower extremities when controlling for sex. Considering the R-2 of the model, other factors not included in the model are also associated with pain in the lower extremities in children with CP.