Objectives: Appropriateness of the geriatric outpatients’ medications needs special attention due to risks of falls, fractures, depression, hospital admissions and mortality. This study aimed to identify current practice on medication usage by using the 2nd version of “Screening Tool of Older People’s Potentially Inappropriate Prescriptions” and “Screening Tool to Alert Doctors to Right Treatment” criteria and affecting factors for the Turkish population. Materials and Methods: This cross-sectional study was conducted between September 2015 and May 2016 at a university research and training hospital’s geriatric outpatient clinic. Patients aged ≥65 years and had ≥5 different prescribed medications (considered as polypharmacy) were recruited. The main outcome measure was the frequency of inappropriate medications identified by clinical pharmacist in the outpatient clinic according to the 2 nd version of the criterion sets. Results: A total of 700 patients (440 female) were included in this study. According to the results, 316 patients (45.1%) with at least one potentially inappropriate medication and 668 patients (98.3%) with at least one potential prescription omission were detected. Potentially inappropriate medications were associated with the number of medications used per patient [odds ratio (OR): 1.20 p<0.001], living alone (OR: 4.12 p=0.02), and having congestive heart failure (OR: 2.41 p<0.001). Twenty-two (27.5%) out of 80 criteria and 4 (11.8%) out of 34 criteria did not apply to the study population. Conclusion: Detecting inappropriate medications to maintain treatment effectiveness is necessary to provide the optimum therapy. Despite the awareness of polypharmacy in outpatient clinics it is still one of the important causes of inappropriate prescription followed by vaccination rate. Therefore, with the contribution of clinical pharmacist using these available criteria is important, moreover modification of these criteria according to the local needs to be considered to achieve better outcomes.