© 2018 Mac Keith Press Aim: We explored factors associated with pain and its severity in a population cohort of young people with bilateral cerebral palsy, comparing parent/carer and young people self-reports. Method: Of 278 survivors (mean age 16y 8mo, SD 1y 4mo, range 13y 8mo–19y 3mo) from the South Thames in the Study of Hips and Physical Experience cohort of 338 young people with bilateral cerebral palsy, 212 parents/carers and 153 young people completed questionnaires on the presence, severity, timing, site, associated factors, impact, and treatment of pain. Results: Seventy per cent of parents/carers reported pain within 3 months, 59% the previous week, and 50% the previous day with 56% reporting ‘regularly experienced’. Of young people able to do so, 63% reported pain within 3 months, 50% the previous week, and 42% the previous day, with 48% reporting regular pain. There was strong agreement between the parent/carer and young people, reporting pain severity over the previous 3 months. Pain severity was associated with increased motor impairment and comorbidity, particularly constipation, spasticity, equipment use, and higher emotional score, but not sex, intellectual disability, speech, or maternal education. Multiple sites of musculoskeletal pain were reported in two-thirds of individuals. Pain was associated with voluntary movement in individuals with less motor impairment and with being moved in those with severe motor impairment. Greater pain severity had a negative effect on both physical and psychological quality of life. Interpretation: Increasing awareness of the comorbidities in cerebral palsy may aid effective treatment, reducing pain experienced by young people with cerebral palsy. What this study adds: Regular moderate or severe pain is reported in young people with bilateral cerebral palsy (CP) in all Gross Motor Function Classification System levels. Pain is reported more frequently in young people who are non-ambulant. General ill health is strongly associated with severity of pain after controlling for severity of CP, especially constipation. Pain occurs most often in ambulant young people during voluntary activity and in those who are non-ambulant when being moved. There is strong agreement between parents/carers and young people about pain presence and severity.