The main objectives were to describe the measures taken by women to detect breast disease prior to invitation to participate in a screening programme for breast cancer, and to identify factors related to non-participation in this programme. A cross-sectional study was designed at the Breast Cancer Early Detection Program of Sabadell-Cerdanyola (BCEDP), using data collected in interviews conducted face to face or over the telephone with 13 760 women participating in the programme and 280 non-participants. A total of 74.2% of the participants versus 70.4% of the non-participants reported having taken measures to detect breast disease, and 71.7% of the participants had undergone mammography versus 69.6% of the non-participants. Of the 10 057 women who had had mammograms, 58% had done so less than 2 years previously. Factors found to be associated to non-participation in the multivariate analysis were: higher level of education, higher occupational skills or working at home, self- or gynaecological examination of breasts, and having received hormone replacement therapy. Higher age group was the only factor that increased the probability of not having undergone mammography previously. Despite the high prevalence of prior measures to detect breast cancer and the similar prevalence between participating and non-participating women, this behaviour is much less prevalent in the group of women 60 years of age or older.