Upper trapezius trigger points can be debilitating and often lead to chronic pain. To determine if long duration low intensity therapeutic ultrasound is effective at treating upper trapezius trigger point pain compared to an inactive placebo treatment. Randomized control trial. Research laboratory. Fifty-one participants (19 males, 32 females, age = 31.8 ± 12.5 y, ht = 168.6 ± 15.9 cm, mass = 77.1 ± 16.1 kg) diagnosed with chronic upper trapezius pain. Participants were randomly assigned into an active (n = 32) or sham (n = 19) treatment group. Treatments were applied at least 3 times a week for 4 weeks and each ultrasound treatment lasted 4 h. Participants completed a daily numeric rating scale (NRS) pain diary. Pain pressure threshold was assessed via a pressure algometer. Repeated-measures ANCOVAs were used to examine differences over time and between groups. Pain on the NRS was significantly reduced from baseline (5.4 ± 1.7) to the conclusion of the study (4.2 ± 1.6) (F4,254 = 7.747, P < 0.001); however, the reduction did not significantly differ between the two groups (F4,254 = 1.096, P = 0.359). There was an average reduction in pain of 1.1 ± 1.8 points over the course of a 4 h treatment (F4,254 = 18.67, P = 0.001), but this reduction did not differ between groups, (F4,254 = 0.701, P = 0.592). Pain pressure threshold improved by 0.46 ± 1.29 and 0.44 ± 1.73 kg for active and sham groups, respectively, but was not different between groups (F2,142 = 1.168, P = 0.314). Four-weeks of low intensity long duration ultrasound reduced upper trapezius trigger point pain, but the improvement is attributed to a placebo effect.