Background: Transcutaneous electrical nerve stimulation (TENS) is widely used for pain management; however, the optimal stimulation intensity remains uncertain. This preliminary observational study investigated the association between TENS current intensity and immediate analgesic effects in patients with lumbosacral pain. Methods: Fifty-three adults with lumbosacral pain undergoing routine physiotherapy were enrolled. Participants were classified post hoc according to their preferred stimulation intensity into a low-intensity group (L, n = 26), receiving stimulation at approximately the sensory threshold level, and a high-intensity group (H, n = 27), receiving stimulation at the highest tolerated intensity. TENS was delivered using an ASTAR ETIUS device (100 Hz, 100 μs, biphasic symmetrical waveform) for 20 min. Pain intensity was assessed before and immediately after treatment using a 10-point Visual Analog Scale (VAS). Between-group baseline characteristics were compared using the Mann–Whitney U test. Within-group changes were assessed using the Wilcoxon signed-rank test, and associations between current intensity and pain reduction were evaluated using Spearman’s rank correlation coefficient (rs). Results: Baseline demographic and clinical characteristics did not differ significantly between groups. No significant change in pain intensity was observed in Group L. In contrast, Group H demonstrated a significant reduction in VAS scores following TENS (VAS before Mdn = 5, VAS after Mdn = 4, Z = 4.11, p < 0.001, effect size r = 0.88). In this group, higher stimulation intensity was associated with greater pain reduction (r_s = −0.48, p = 0.011). Conclusions: In this study, TENS delivered at the highest tolerated intensity was associated with greater immediate pain relief than stimulation applied near the sensory threshold. Because of the observational design, post hoc group allocation, and lack of randomization, the findings should be interpreted as exploratory and hypothesis-generating. Further randomized controlled trials are needed to determine whether higher stimulation intensities causally improve TENS analgesic efficacy.