This paper discusses how the activity and expression of cyclooxygenases are influenced by vanadium compounds at anticancer concentrations and recorded in inorganic vanadium poisonings. We refer mainly to the effects of vanadate (orthovanadate), vanadyl and pervanadate ions; the main focus is placed on their impact on intracellular signaling. We describe the exact mechanism of the effect of vanadium compounds on protein tyrosine phosphatases (PTP), epidermal growth factor receptor (EGFR), PLC gamma, Src, mitogen-activated protein kinase (MAPK) cascades, transcription factor NF-kappa B, the effect on the proteolysis of COX-2 and the activity of cPLA(2). For a better understanding of these processes, a lot of space is devoted to the transformation of vanadium compounds within the cell and the molecular influence on the direct targets of the discussed vanadium compounds.