Despite, several studies demonstrating pro-metastatic effects of the metalloproteinase ADAMTS1 in breast cancer, its role in facilitating the metastatic cascade remains unclear. To date there have been limited studies that have examined the expression of ADAMTS1 in primary and metastatic breast cancer tissues.We assessed ADAMTS1 mRNA levels in publically available breast cancer sets and analysed ADAMTS1 protein levels by immunohistochemistry in breast tissue microarrays containing normal breast tissue (n=9), primary invasive ductal breast carcinomas (n=79) and metastatic lesions (n=58). To understand the underlying events influenced by ADAMTS1 and provide a mechanism by which tumors expressing this protease promote metastasis, we assessed the ability of PyMT/Adamts1+/+, PyMT/Adamts1+/- and PyMT/Adamts1-/- primary mammary cancer cells to adhere to matrigel and migrate or invade towards a chemoattractive environment.High ADAMTS1 expression was associated with reduced disease-free survival, distant metastasis free-survival and overall survival in breast cancer patients with node negative disease. Although ADAMTS1 expression was reduced in primary breast cancers compared to normal tissue and not elevated in metastatic lesions, high ADAMTS1 immunostaining was associated with a higher number of positive lymph nodes (p=0.006) and the presence of distant metastasis (p=0.023). Depletion of Adamts1 in mammary cancer cells impeded their adhesion to a biological matrix substratum and diminished cell migration but not invasion.The effects observed on cell adhesion and migration demonstrates a potential mechanism whereby ADAMTS1 promotes breast cancer metastasis.