Breast cancer is the most common female cancer and the commonest cause of death due to cancer for women in Malaysia. This study was performed to identify the relationship with lifestyle factors. A case-control study was conducted among females with breast cancer who came for treatment to the Breast Clinic Hospital Kuala Lumpur in July until September 2004. A total of 203 female patients were recruited as cases along with 203 patients who attended the Outpatient Clinic, Hospital Kuala Lumpur during the study period as the controls. The study showed women who did not exercise regularly to have four times higher risk (adjusted odds ratio is 3.49, 95% CI is 1.84 to 6.62) compared to those who exercised regularly. Women with a high fat diet were also at elevated risk (adjusted odds ratio 3.84, 95% CI is 1.20 to 12.34) compared to those consuming a low fat diet. Woman without breast cancer generally had a longer duration of lifetime lactation with a median of thirty-three months compared to woman with breast cancer (twenty months, p<0.05). Women who did not take oral contraceptive pills but had breast-fed their child have a 56.0% lower risk (crude odds ratio 0.44, CI is 0.22 to 0.87) compared to women who did not take oral contraceptive pill and also did not breast-fed their child. If they had breast fed for thirteen months and above, they faced a 61.0% lower risk (crude odds ratio 0.39, 95% CI is 0.17 to 0.87). There was a significant inverse trend for lifetime lactation and breast cancer risk. In conclusion certain life styles of women are associated with a higher risk of breast cancer development. Therefore, the promotion of a healthy life style should be emphasized.