As an emerging persistent organic pollutant (POP), perfluorooctanoate (PFOA) is one of the most abundant perfluorinated compounds (PFCs) in the environment. This review summarized the molecular mechanisms and signaling pathways of PFOA-induced toxicity in animals and humans as well as their implications for health risks in humans. Traditional PFOA-induced signal pathways such as peroxisome proliferating receptor alpha (PPARα), constitutive androstane receptor (CAR), farnesoid X receptor (FXR), and pregnane-X receptor (PXR) may not be important for PFOA-induced health effects on humans. Instead, pathways including p53/mitochondrial pathway, nuclear lipid hyperaccumulation, phosphatidylinositol 3-kinase-serine/threonine protein kinase (PI3K-AKT), and tumor necrosis factor-α/nuclear factor κB (TNF-α/NF-κB) may play an important role for PFOA-induced health risks in humans. Both in vivo and in vitro studies are needed to better understand the PFOA-induced toxicity mechanisms as well as the associated health risk in humans.