BACKGROUND: In breast cancer, there is an inverse relationship between HER2/neu overexpression and receptors for estrogen (ER) or progesterone (PR). Some clinical observations such as the age-related association between hormone receptors and tumour grade, which predicts HER2/neu overexpression, suggest an age-related relationship. PATIENTS AND METHODS: Our study population consisted of 1362 consecutive women receiving primary surgery for non-metastatic invasive breast cancer. We compared the relationship between both hormone receptors and HER2/neu overexpression in different age groups taking other tumour characteristics into account. RESULTS: In a multivariate model, considering the overall group, a negative ER, a negative PR and a high tumour grade were predictive for HER2/neu overexpression (P <0.001). Considering 246 women aged < or =45 years, the only predictor for HER2/neu overexpression in this age category was a high tumour grade (P = 0.003). Considering the 1116 women aged >45 years, ER (P = 0.001), PR (P = 0.001) and tumour grade (P <0.001) were associated with HER2/neu (P <0.001). CONCLUSION: Our findings indicate that the association between ER, PR and HER2/neu overexpression varies with age. The hormone receptors are not an independent predictor for the HER2/neu status in young women while they are in elder patients.