OBJECTS:Optic nerve sheath diameter has been linked with intracranial pressure in previous studies. Measurement of sheath diameter using transorbital ultrasound is proposed as a clinical assessment indicator of developing hydrocephalus in the paediatric population. METHODS:A retrospective review of optic nerve sheath ultrasound examinations performed in a clinical setting between 2000 and 2006 for assessment of hydrocephalus in a single institution. RESULTS:A total of 331 examinations were performed in 160 patients over the study period. A satisfactory image was possible in all cases. Sheath diameters were correlated with clinical case data from concurrent case records. CONCLUSION:Transorbital ultrasound is a reproducible, non-invasive technique for the assessment of optic nerve sheath diameter and is well tolerated in children. Our series revealed asymptomatic baseline value higher than in previous reports. Variation from individual case asymptomatic baseline was the most sensitive variable in the series in determining development of hydrocephalus. This technique is felt to be a useful adjunct in the assessment of hydrocephalus in the paediatric neurosurgical population.