Whiplash injuries (WLs) are the most frequent cause of emergency room visits after motor vehicle collisions. In clinical practice, massage, electrotherapy, mobilization, or therapeutic exercise are used. As part of manual therapy, high-velocity, low-amplitude manipulative techniques can also be used. Objectives: To evaluate the effect of the cervical Specific Adjustment Technique (SAT) in adults affected by whiplash on pain, functionality, cervical mobility, and radiological changes in cervical curvature through a prospective, single-blind, randomized clinical trial. Methods: One hundred and nineteen patients with grade II acute WL were randomly assigned to either the manipulation group (MAN group = 59) or the rehabilitation group (RHB group = 60) to receive 3 or 20 sessions of treatment, respectively. Both groups were measured at baseline and 15, 30, and 120 days after starting treatment. Results: Statistically significant differences were found in the MAN group in flexion (p = 0.041) and left-side bending (p = 0.022); similar statistical values were found in the other measures. According to the interaction treatment-time effect, statistical significance for the Cobb angle was obtained in the MAN group (p = 0.047). Conclusions: the effects of SAT were comparable in terms of pain, functionality, and mobility of the cervical spine. Although further research is needed on its effects in the acute phase, due to its effectiveness and lower associated cost, SAT could be considered a useful technique, at least during the first 3 months after a traffic collision.