Hospital-based studies have reported long delays in the diagnosis of paediatric brain tumours. Our objective was to describe the duration between onset of symptoms and diagnosis of medulloblastoma in children and study their clinical determinants in a population-based study. This retrospective cohort study included all paediatric medulloblastoma from a region of France from 1990 to 2005. The median interval from symptom onset until diagnosis for these 166 patients was 65 days and did not decrease during the study period. The most frequent manifestations were: vomiting (88%), headaches (79%), psychomotor regression (60% of children under 3 years), psychological symptoms (27%), strabismus (26%), and asthenia (25%). For one third of the children under 3 years, the diagnosis was made only after life-threatening signs of intracranial hypertension appeared. The prediagnosis interval was significantly longer (median 91 vs. 60 days, p = 0.001) in children with psychological symptoms (27%). Causes for intervals that exceeded the median (65 days) included inconsistent (25%) or late (36%) combination of headaches and vomiting, a period of spontaneous symptom remission (14%-20%), no (24%) or late (57%) neurological signs, psychological symptoms (35%), and a normal neurological examination (27%). Time to medulloblastoma diagnosis in children remains fairly long, despite advances in imaging. Primary-care physicians must be suspicious not only of suggestive neurological signs, but also of non-specific symptoms that persist or are multiple. A meticulous neurological examination and cerebral imaging for such patients might facilitate earlier diagnosis.