OBJECTIVE: Prevalence of asthma and overweight has increased simultaneously during the past decades. Several studies have reported an association between these two health problems, but it is unclear whether this relation is causal. We hypothesize that children with asthmatic symptoms are less physically active, which may contribute to the development of overweight. PATIENTS AND METHODS: The study included children from the KOALA Birth Cohort Study who were invited at 4 to 5 years of age to wear an Actigraph accelerometer for 5 days (n = 305; 152 boys). Information on wheezing was gathered by repeated questionnaires completed by parents at child ages 7 months and 1, 2, and 4 to 5 years. Questionnaires on physical activity were completed at child age 4 to 5 years, and height, weight, and abdominal circumference were measured. Accelerometer data were expressed as mean counts per minute, minutes per day performing vigorous activity, and moderate-to-vigorous physical activity during > or = 1 minute. RESULTS: Children who had wheezed in the last 12 months showed very similar activity levels compared with children who had never wheezed. By contrast, boys who had wheezed at least once but not in the last 12 months were more physically active than boys who had never wheezed (geometric mean: 694 vs 625 cpm; adjusted geometric mean ratio: 1.11). This was not found for girls. Similar results were found in parent-reported physical activity data. No association was found between wheezing at any age and overweight at the age of 4 to 5 years. CONCLUSIONS: These results do not support our hypothesis and previous studies that showed that wheezing children are less physically active. Our data provide no evidence that asthmatic symptoms induce a lower physical activity level and more overweight. Additional research could concentrate on the effect of physical activity and overweight on the development of asthmatic symptoms.