The CCN family members cysteine-rich 61 (Cyr61/CCN1), connective tissue growth factor (CTGF/CCN2) and nephroblastoma over-expressed (Nov/CCN3) play diverse roles in cells, are known to regulate cell growth, adhesion, matrix production and migration and are involved in endocrine-regulated pathways in various cell types. The role of these molecules in cancer remains controversial. In a cohort of 122 human breast tumours (together with 32 normal breast tissues) we have analysed the expression of all three CCN members at the mRNA and protein levels. Significantly higher levels of Cyr61 (P = 0.02), but low levels of CTGF and Nov, were seen in tumour tissues compared with normal tissues. Significantly raised levels of Cyr61 were associated with poor prognosis (P = 0.02), nodal involvement (P = 0.03) and metastatic disease (P = 0.016). Patients who died of breast cancer also had high levels of Cyr61. In contrast, CTGF in patients with poor prognosis (P = 0.021), metastasis (P = 0.012), local recurrence (P = 0.0024) and mortality (P = 0.0072) had markedly reduced levels. Similar to CTGF, low levels of Nov were also seen in patients with poor prognosis and mortality and with significantly decreased survival (P = 0.033 and P = 0.0146, respectively). This result was fully supported by immunohistochemical analysis of frozen sectioned tissues. While fibroblasts and endothelial cells generally expressed good levels of all three CCN proteins, highly invasive MDA MB 231 cells expressed lower levels of CTGF and Nov, but higher levels of Cyr61, than the less invasive MCF-7. It is concluded that members of the CCN family are differentially expressed and may play important but contrasting roles in the progressive nature of human breast cancer. While Cyr61 appears to act as a factor stimulating aggressiveness, CTGF and Nov may act as tumour suppressors.