Perfluoro-n-octane is a high-density liquid perfluorocarbon used as a long-term vitreous replacement in vitreoretinal surgery. In this study, we assessed the toxicity of perfluoro-n-octane (PFOC) on Vero cells using an indirect toxicity test, scanning electron microscopy and immunocytochemistry. For indirect toxicity test, Vero cells were cultured for 12 h with PFOC extracts in 96-well plates and the plates were, then, read at 540 nm. For direct toxicity, Vero cells were incubated with 0.1 ml of perfluoro-n-octane alone. Glass coverslips were used as inert control for weight, to produce mechanical compression similar in weight and area to that caused by perfluoron- octane. Cells cultured without PFOC were used as a negative control. Silicone bands with a weight and area similar to those of perfluoro-n-octane served as a positive control for toxicity. The indirect toxicity test showed that perfluoro-n-octane did not release soluble toxic substances that affected cell growth. In the direct toxicity test, the cells in the control group had homogenously distributed actin filaments, although scanning electron microscopy revealed some vesicles on the cell surface. In the controls for weight, cytoplasmic retraction and the formation of thin cellular prolongations were seen. Cells incubated with perfluoro-n-octane showed greater changes compared to those seen in cells under a similar control weight. Silicone-treated cells had an irregular or fragmented morphology. These results show that, in addition to its compressive action on cultured cells, perfluoron- octane may also exert a toxic effect.