Hip fractures are among the most important causes of ill health and death among elderly people. Several potentially modifiable risk factors have been reported. Most claimed physical activity as a promising, inexpensive preventive measure for hip fracture. However, knowledge about risk factors for hip fracture in Asian populations is very limited. We therefore conducted a case-control study to assess the relationships between physical activity and risk of hip fractures in Thai women. From 14 hospitals in Thailand, 229 cases with a radiologically confirmed first hip fracture were enrolled. Two hundred and twenty-four controls were randomly recruited from the same neighborhood and were matched to the cases by age within a 5 year range. Information on physical activity as well as other potential confounders was obtained through personal interviews. Multivariate logistic regression revealed that past physical activity was protective in both very active and active women (OR = 0.67, 95% CI = 0.40-1.12 for moderately active women and OR = 0.20, 95% CI = 0.10-0.38 for very active women; p value for trend < 0.01). Recent physical activity reduced the risk to about two-thirds (OR = 0.33, 95% CI = 0.19-0.60 and OR = 0.35, 95% CI = 0.18-0.69 for moderately and very active women respectively). In addition, breastfeeding was identified to be a protective factor (OR = 0.87, 95% CI = 0.80-0.94). In contrast, the following risk factors were identified: current use of antihistamine (OR = 13.96, 95% CI = 1.38-141.13) or traditional medicine (OR = 7.66, 95% CI = 2.71-21.63), underlying cerebrovascular diseases (OR = 6.53, 95% CI = 2.10-20.34), history of fracture (OR = 4.04, 95% CI = 1.26-12.99), parental Chinese racial background (OR = 2.52, 95% CI = 1.49-4.23), alcohol consumption (OR = 2.30, 95% CI = 1.04-5.09).