To investigate the role of diet and other lifestyle factors in the incidence of overactive bladder and stress incontinence in women. Studies have suggested relationships between different aspects of lifestyle and symptoms of urinary incontinence, but there is a lack of firm evidence about their role in its cause. A random sample of women aged >or= 40 years living at home took part in a prospective cohort study. Baseline data on urinary symptoms, diet and lifestyle were collected from 7046 women using a postal survey and food-frequency questionnaire. Follow-up data on urinary symptoms were collected from 6424 of the women in a postal survey 1 year later. Logistic regression was used to investigate the association of food and drink consumption and other lifestyle factors with the incidence of overactive bladder and stress incontinence. In the multivariate model for the onset of an overactive bladder, there were significantly increased risks associated with obesity, smoking and consumption of carbonated drinks, and reduced risks with higher consumption of vegetables, bread and chicken. Obesity and carbonated drinks were also significant risk factors for the onset of stress incontinence, while consumption of bread was associated with a reduced risk. Causal associations with obesity, smoking and carbonated drinks are confirmed for bladder disorders associated with incontinence, and additional associations with diet are suggested. Behavioural modification of lifestyle may be important for preventing and treating these disorders.