SUMMARYThe use of atypical antipsychotics in children and adolescents has increased in recent years. A 16-year-old male patient reported that he had used paliperidone for 3 years and had gained weight during this period. Various laboratory tests were performed when the patient started treatment in our clinic. It is evident from the test result that 3-year use of paliperidone dramatically increased fasting blood sugar, total cholesterol, low-density lipoprotein, triglycerides and prolactin levels in the patient. The metabolic parameters of the patient decreased into the normal range once the medication was stopped. Thus, paliperidone should be used carefully based on the side effects for patients under 18 years of age.