There has been conflicting evidence on the impact of bilateral breast cancer (BBC) on the survival and management of patients. The objectives of this study were to address the incidence of BBC and to investigate its characteristics and outcome compared to unilateral cancer. Data were acquired from the prospectively maintained NUIG breast cancer database between 1988 and 2008. BBC were then categorized as synchronous (within 12 months) or metachronous (after 12 months of first tumour). SPSS was used for data analysis. The incidence of BBC in our population was 4.4% (112 of 2,524). Of those 2.1% were synchronous while 2.3% were metachronous. Compared to unilateral cases, bilateral cancer patients were younger (P = 0.021) and had smaller size (P = 0.001) and earlier stage (P < 0.001) tumours at diagnosis. We identified the HER2/neu positivity as a risk factor for developing contralateral breast tumour and ER negativity as a risk factor for developing metachronous tumours. While there was no significant difference in survival for patients with bilateral compared to unilateral tumour (P > 0.05), the synchronous tumour was associated with poorer survival (P = 0.010) in comparison to metachronous tumour. This large single-institutional experience does not support the increasing practice of prophylactic mastectomy but does justify regular follow-up with mammography for early detection of contralateral tumour.