Objective: To examine women's weight control practices and their effectiveness in preventing weight gain. Design: Retrospective cohort study of weight control practices and 2-year weight change among mid-age women participating in the Australian Longitudinal Study on Women's Health (ALSWH). Subjects: 11 589 Australian women (aged 47-52 years). Measurements: The prevalence and types of self-reported weight control practices used were assessed by a nine-item instrument. Two-year weight change was self-reported and adjusted for baseline body mass index (BMI) and other potential confounders. Results: Seventy-four per cent of the cohort (N=8556) reported actively trying to control their weight. Dietary modification was used more frequently than exercise. Two-thirds of the weight-controlling women used a combination of practices, the two most common being 'decreased food quantity, cut down on fats/sugars and exercise' (32%, baseline BMI 25.87(0.10)), and 'decreased food quantity and cut down on fats/sugars without exercise' (15.6%, baseline BMI 27.04(0.14)). Potentially health-damaging practices (smoking, laxatives, fasting) were relatively uncommon, at 7.9%. Only one combination of practices (decreased food quantity, cut down on fats/sugars, use of a commercial weight loss programme and exercise) prevented mean weight gain (-0.03 kg), whereas the mean (s.d.) weight of the cohort increased (+1.19(4.78)) over the 2-year period. Conclusions: The majority of mid-age women attempting weight control used practices consistent with public health messages. Despite their efforts, the group was mostly unsuccessful in preventing weight gain. Public health authorities and health practitioners may need to make more quantitative recommendations and emphasize the importance of balancing physical activity with dietary intake to achieve successful weight control for women at this life stage.