Background: The issue of icodextrin biocompatibility is somehow ambiguous. Whereas some experimental data point at better bicompatibility of icodextrin compared with high glucose concentration fluid, other reports showed substantial cytotoxic effects upon monocytes and cultured mesothelial cells. The present investigation exposes the first attempt to investigate the biocompatibility issue in an in vivo and in situ setup. Methods: Mice were intraperitoneally injected once a day with the 7.5% icodextrin solution, during 30 consecutive days. Imprints of the mesothelial monolayer covering the anterior liver surface were taken after 2 h, 15 and 30 injections, as well as after recovery periods of 7, 30 and 60 days. Changes on the cell population were evaluated as a function of: density, cell surface area, cell radius, nuclear surface area, number of nucleoli per nucleus, nuclear cytoplasmic index, as well as for prevalence of multinucleation, mitosis, non-viable cells and apoptotic bodies. Additionally, peritoneal dialysis was performed in 3 groups of rats exposed to 4.25% glucose dialysis fluid, 1.1% amino acids solution, or to 7.5% icodextrin. Samples were taken for thiobarbituric acid reactive substances (TBARS) from each group. Results: Mesothelial cell populations of mice exposed to 7.5% icodextrin displayed significantly reduced density, increased cell size, higher increased nuclear/cytoplasmic index, increased numbers of heterogeneous nucleoli, extremely low prevalence of mitosis, atypical mitosis, micronuclei, reduced cell viability as well as a significantly higher prevalence of apoptosis. Rats exposed to the same experimental solution showed significantly higher levels of TBARS (basically malondialdehyde), testifying for an undergoing process of lipid peroxidation. Conclusions: Overall, these results suggest that the 7.5% icodextrin dialysis solution induced, through a mechanism of lipid peroxidation, substantial DNA injury, leading the exposed monolayer to commit protective cellular suicide. Consequently, this information raises some doubts about the safety of 7.5% icodextrin solution in peritoneal dialysis patients.