Aim: There are reports that isotretinoin causes some important diseases such as teratogenicity, inflammatory bowel disease and sacroiliitis by triggering inflammation. (Monocyte/HDL (high density lipoprotein) ratio) MHR is closely related to inflammation and is thought to be an indicator of atherosclerotic development. We aimed to investigate how isotretinoin (ISO) affects the immunoinflammatory response in acne patients.Materials and Methods: In this study, 116 nodulocystic acne patients who received ISO treatment for at least three months were evaluated retrospectively. ISO treatment was given to patients at a dose of 0.5–1 mg/kg. Pre-treatment and post-treatment white blood cell (WBC), neutrophil, lymphocyte, monocyte, platelet, mean platelet volume (MPV), platelet, plateletcrit, platelet distribution width (PDW), neutrophil lymphocyte ratio (NLR), platelet lymphocyte ratio (PLR), total cholesterol, LDL cholesterol, triglyceride, HDL cholesterol and MHR were evaluated.Results: MPV and MHR values were significantly increased after 3 month treatment (p < 0.05). There was no significant change in NLR and PLR values (p > 0.05). There was a significant decrease in neutrophil count (p < 0.05). There were no significant changes in WBC, lymphocyte, monocyte, platelet, plateletcrit values (p > 0.05). Total cholesterol, LDL cholesterol and triglyceride levels were significantly increased after three months of treatment (p < 0.05). HDL cholesterol levels decreased significantly after three months of treatment (p < 0.05).Conclusion: We concluded that ISO treatment may trigger inflammation due to the increase in MPV and MHR value. MHR can show inflammation after ISO treatment.