["Abnormalities in distal growth and low levels of insulin-like growth factor (IGF)-I have been reported in children with Perthes' disease. Our aim was to establish whether the acute phase of Perthes' disease is associated with abnormalities of growth, of bone or of collagen turnover.", 'We performed a cross-sectional study of 15 children (3-11 years of age, 13 boys) at acute presentation and a longitudinal cohort study of 9 children. We measured (1) the lengths of both lower legs (by knemometry) at weeks 1, 2, 6 and 12, (2) height and weight at presentation and at the second-year follow-up, and (3) levels of IGF-I, IGFBP-3, collagen markers and bone alkaline phosphatase at weeks 1 and 12, and in year 2.', 'Height SD scores were normal at presentation but declined thereafter. Lower leg growth was not impaired at presentation but was asymmetrical, ceased during weeks 2-6, and then resumed symmetrically. Patients had persistently low IGF-I, low soft tissue collagen synthesis and enhanced collagen breakdown compared with age- and sex-related reference data. Markers of bone formation increased during follow-up.'] Do children with acute Perthes ' disease have asymmetrical lower leg growth and abnormal collagen turnover?