Purpose: This study evaluated the effects of frailty on postoperative opioid consumption in elderly patients. Methods: Patients aged 65 and older scheduled for unilateral primary total knee arthroplasty under spinal anesthesia were included. A blinded anesthesiologist assessed patients using the FRAIL scale during the preoperative visit, classifying them into robust (Group I), pre-frail (Group II), and frail (Group III) categories. The main outcome measure was total opioid consumption over 24 h. Opioid consumption was recorded at 6 (T1), 12 (T2) and 24 (T3) hours postoperatively. Secondary outcomes included visual analog pain scores (VAS) at rest (VAS-R) and during 45° knee flexion (VAS-F), as well as postoperative nausea and vomiting. Results: Seventy-five patients were included in the study, with seventy-three completing it and two being excluded. Total opioid consumption was significantly higher in Groups II and III compared to Group I (p < 0.001 for both). There were no significant differences in VAS-R scores between groups at T0, T1, T2, and T3 (p = 0.659, p = 0.425, p = 0.994, and p = 0.689, respectively), and no significant differences in VAS-F scores at the same time points (p = 0.580, p = 0.739, p = 0.322, and p = 0.679, respectively). Conclusion: Our study results indicate that frailty, easily assessed preoperatively in elderly surgical patients, is a significant predictor of postoperative opioid consumption.