Breast cancer is the most common cancer in women in industrialized countries. Environmental factors, such as differences in diet are likely to have an important influence on cancer emergence. Among these factors, n-3 polyunsaturated-fatty acids, such as docosahexaenoic acid (DHA), are good candidates for preventing breast cancer. Here we investigate the effect of DHA on the human breast cancer cell line MDA-MB-231 and show that DHA incorporation i) has an anti-proliferative effect, ii) induces apoptosis via a transient increase in caspase-3 activity and the promotion of nuclear condensation, and iii) reduces the invasive potential of MDA-MB-231 cells. To conclude, DHA may have beneficial effects as a result of slowing the proliferation of tumor cells, and minimizing their metastatic potential.