Caveolin-1 is the principal constituent protein of caveolae, which are specialised plasma membrane invaginations with diverse biological roles. Caveolin-1 is suggested to have tumour suppressive functions and CAV1 gene mutations have been reported in 20% of breast cancers. The aim of the present study was to evaluate the frequency of CAV1 mutations in a large cohort of optimally accrued breast cancers. Two independent series of breast cancer samples were analysed: 82 fresh-frozen grade 3 and 158 formalin-fixed paraffin-embedded invasive ductal carcinomas of no special type were consecutively accrued and subjected to microdissection of neoplastic epithelial cells prior to DNA extraction. Thirty-nine human breast cancer cell lines were also included in this study. The trans-membrane region of CAV1 and adjacent sequences, where mutations are reported to cluster, were amplified by PCR, followed by direct sequencing and mutational analysis. None of the reported CAV1 gene mutations, including CAV1 (P132L), were identified in either clinical samples (95% CI: 0-1.5%) or human breast cancer cell lines analysed. One novel non-synonymous germline polymorphism was detected within a reported region of high mutational frequency. This study does not corroborate the reported frequent occurrence of CAV1 gene mutations, including CAV1 (P132L), in primary human breast carcinomas. Our findings demonstrate that if CAV1 mutations do exist, their overall mutational frequency is substantially lower than positive reports have suggested. Taken together with other studies, which have also failed to identify CAV1 mutations, our data call into question the existence and biological and clinical relevance of CAV1 gene mutations in human breast cancer.