Because the criteria used for diagnosing between generalized joint hypermobility (GJH) and musculoskeletal complaints, as well as relations between GJH and an insufficient motor development and/or a reduced physical activity level differ, the prevalence of GJH varies considerably. The aim of this study was to survey the prevalence of GJH defined by a Beighton score at >or=4, >or=5, or >or=6 positive tests of 9 and benign joint hypermobility syndrome (BJHS) in Danish primary school children at 8 years of age. A second aim was to compare children with and without GJH and BJHS regarding motor competence, self-reported physical activity, and incidence of musculoskeletal pain and injuries. A cross-sectional study of 524 children in the second grade from 10 public schools was performed. A positive response rate was obtained for 416 (79.4%) children, and 411 (78.4%) children were clinically examined and tested for motor competence, whereas questionnaire response to items comprising musculoskeletal pain and injuries, in addition to daily level and duration of physical activity, corresponded to 377 (71.9%) children. In total, 29% of the children had GJH4, 19% had GJH5, 10% had GJH6, and 9% had BJHS, with no gender difference. There was no difference in daily level and duration of physical activity and in frequency of musculoskeletal pain and injuries between those with and without GJH. Children with >or=GJH5 as well as with >or=GJH6 performed better in the motor competence tests. Motor competence and physical activity are not reduced in primary school children at 8 years of age with GJH or BJHS. It is recommended that a potential negative influence on the musculoskeletal system over time, as a result of GJH, be investigated by longitudinal studies.