Objective: This project determined the location and distribution of cavitations (producing vibrations and audible sounds) in the lumbar zygapophyseal (Z) joints that were targeted by spinal manipulative therapy (SMT). Methods: This randomized, controlled, clinical study assessed 40 healthy subjects (20 men, 20 women) 18 to 30 years of age who were block randomized into SMT (group 1, n = 30) or side-posture positioning only (group 2; control, n = 10) groups. Nine accelerometers were placed on each patient (7 on spinous processes/sacral tubercles of L1-S2 and 2 placed 3 cm left and right lateral to the L4/L5 interspinous space). Accelerometer recordings were made during side-posture positioning (groups 1 and 2) and SMT (group 1 only). The SMT was delivered by a chiropractic physician with 19 years of practice experience and included 2 high-velocity, low-amplitude thrusts delivered in rapid succession. Comparisons using χ(2) or McNemar test were made between number of joints cavitating from group 1 vs group 2, upside (contact side for SMT) vs downside, and Z joints within the target area (L3/L4, L4L5, L5/S1) vs outside the target area (L1/L2, L2/L3, sacroiliac). Results: Fifty-six cavitations were recorded from 46 joints of 40 subjects. Eight joints cavitated more than once. Group 1 joints cavitated more than group 2 joints (P < .0001), upside joints cavitated more than downside joints (P < .0001), and joints inside the target area cavitated more than those outside the target area (P < .01). Conclusions: Most cavitations (93.5%) occurred on the upside of SMT subjects in segments within the target area (71.7%). As expected, SMT subjects cavitated more frequently than did subjects with side-posture positioning only (96.7% vs 30%). Multiple cavitations from the same Z joints had not been previously reported.