PURPOSE. To investigate whether time outdoors and a range of other activities are associated with change in spherical equivalent (SE) and axial length in Chinese children over a period of 2 METHODS. A total of 1997 children aged 12.7 +/- 0.5 (10.9-15.6) years in the Anyang Childhood Eye Study (ACES) were examined annually (baseline and two follow-up visits). Myopia was defined as cycloplegic SE < -0.50 diopters (D). Questionnaires were administered to the students and parents at baseline to gauge time spent outdoors and on other tasks. We ran mixed linear models including age, sex, and years of follow-up. RESULTS. In the full cohort of children there was a suggestive association between time spent outdoors and change in axial length; however, the effect size was very small (high versus low tertile: -0.016 mm/y, P = 0.053). The association was observed in children not myopic at baseline (high versus low tertile, -0.036 mm/y; P = 0.009) but not in those already myopic at baseline (high versus low tertile: -0.005 mm/y; P = 0.595). Time outdoors and change in SE showed similar, but nonsignificant, relationships (P > 0.05), perhaps due to insufficient statistical power. The other activities examined and parental myopia were not associated with changes in SE and axial length (P > 0.11). CONCLUSIONS. Within the normal range of variation encountered in these Chinese children, a wide range of activities were largely unrelated to myopia progression at this age. However, there was suggestive evidence that greater time outdoors was associated with slower axial elongation in nonmyopic teenagers, but not in existing myopes.