A population-based study of children with hemiplegic cerebral palsy (CP) was performed to investigate whether thrombophilic tendencies are implicated in the aetiology of the condition. Thirty-eight children (23 males, 15 females; mean age 8.7 years, SD 4.1 years) with hemiplegic CP were ascertained. Twenty-seven children (18 males, nine females; mean age 8.4 years, SD 4.3) gave consent for inclusion. The non-study group comprised five males and six females; mean age 9.4 years, SD 4.1. In six children, seven thrombophilic ‘abnormalities’ were identified. Five of these abnormalities were of an equivocal nature and probably did not represent true clinical thrombophilia; reasons for this interpretation are discussed. Contrary to other published non-population-based studies, we have not shown an association between thrombophilia and hemiplegic CP. More studies, including maternal studies, are required to explore this complex subject further.