This study was undertaken to investigate the evolution of clinical features between onset of symptoms and diagnosis in children with brain tumours and to identify ways of shortening the time to diagnosis. One hundred and thirty-nine children with a brain tumour were recruited from four UK paediatric neuro-oncology centres. Children had a median of one symptom or sign at symptom onset and six by diagnosis. The symptoms and/or signs experienced at symptom onset and at diagnosis were as follows: headache in 55 and 81 children, nausea and vomiting in 39 and 88 children, motor system abnormalities in 31 and 93 children, cranial nerve palsies in 24 and 75 children, visual system abnormalities in 23 and 96 children, endocrine or growth abnormalities in 10 and 35 children and behavioural change in 4 and 55 children. The median time between symptom onset and diagnosis (symptom interval) was 3.3 months. A longer symptom interval was associated with head tilt, cranial nerve palsies, endocrine and growth abnormalities and reduced visual acuity. More than half of children with brain tumours developed problems with vision and more than a third developed motor problems, cranial nerve palsies, behavioural change, or nausea and vomiting between symptom onset and diagnosis.