It is well-known that problems related to pharmacotherapy affect pediatric patients' therapy outcomes. Evaluating pharmacotherapy by a clinical pharmacist in pediatric clinics could ameliorate drug-related problems (DRPs). This study aimed to identify and compare the prevalence and types of DRPs in pediatric patients in two study phases: the prospective phase while providing clinical pharmacist-led medication review service and the retrospective phase among subjects obtained by age-sex-diagnose-matching according to the prospective phase. This observational study consisted of two phases (the prospective part between June 2019 and February 2020 and the retrospective part between December 2018 and February 2019) and was conducted in a pediatric unit of a university hospital. Turkish version of Pharmaceutical Care Network Europe Foundation Classification V9.1 is used to identify DRPs. Lexicomp® and Micromedex® were the resources used to assess the potential drug-drug interactions. Medscape® and UpToDate® recommendations and evidence-based guidelines were applied in assessing compliance with approved pharmacotherapy of patients. Prevalence and types of DRPs and clinical pharmacist interventions were assessed. Among 174 patients, at least one DRP was seen in 78,16% of the patients, and 527 DRPs were identified. Some of the problems were related to drug-drug interaction (64,90%), therapeutic monitoring (11,39%), and dosing (11,01%). Antiinfectives, bronchodilators, and inhaled corticosteroids were the most frequently used drugs. There were significant differences in duration of hospitalization (p=0,025), number of drugs used (p=0,003), and total DRPs (p=0,019) between the study and control groups. The findings demonstrate the potential to detect DRPs through pharmacist involvement in direct patient care.