Many children are admitted to hospital for treatment of an acquired gait disorder. Some gait disorders have a definite underlying physical cause and some are idiopathic. A literature review shows that there have been few attempts to estimate the incidence or prevalence of idiopathic gait disorder in children. The economic and social impact may be substantial with regard to therapy and investigations and school absence, respectively. This study attempted to estimate the incidence and impact of idiopathic gait disorder in a tertiary children's hospital. It evaluated prospectively all the children admitted with a gait disorder requiring physiotherapy treatment at Birmingham Children's Hospital, using a standardized pro-forma, during a 3-month period between March-June 1999. One hundred and three children (aged 2-16 years) were admitted with gait disorders (57 female and 46 male). Eight had an idiopathic gait disorder. All eight children exhibited significant functional impairment, pain and school absence. Idiopathic gait disorder accounted for 8% of children admitted to hospital with an acquired gait disorder and had an annual incidence of at least 2-4 per 100,000 children. The economic and social impact of these disorders is, therefore, substantial, especially with regard to diagnosis, investigations, treatment and school absence.