Background: Non-ST-segment elevation acute myocardial infarction (NSTEMI) represents a heterogeneous patient population with varying risks of adverse outcomes. The RISK-PCI score, initially developed for ST-segment elevation myocardial infarction (STEMI) patients, was evaluated for its prognostic value in NSTEMI patients undergoing percutaneous coronary intervention (PCI). Methods: A retrospective observational study of 242 NSTEMI patients treated with PCI at the Clinical Center of Serbia from June 2011 to June 2016 was conducted. The RISK-PCI score, incorporating clinical, echocardiographic, and angiographic variables, was calculated for each patient. The primary outcome was 30-day major adverse cardiovascular events (MACE). Secondary outcomes included individual components of MACE. Statistical analyses were performed to assess the predictive value of the RISK-PCI score. Results: The primary outcome of 30-day MACE occurred in 9.9% of patients. Independent predictors of 30-day MACE included age > 75 years, glucose ≥ 6.6 mmol/L, creatinine clearance < 60 mL/min, and post-procedural TIMI flow < 3. The RISK-PCI score demonstrated good discrimination for 30-day MACE (AUC = 0.725). Patients stratified into the very high-risk group (RISK-PCI score ≥ 7) had significantly higher risks of 30-day MACE (29.4%). Conclusions: The RISK-PCI score effectively stratifies NSTEMI patients by their risk of 30-day MACE, identifying a very high-risk subgroup that may benefit from closer monitoring and tailored interventions. External validation on larger cohorts is recommended to confirm these findings.