A 21-year-old female National Collegiate Athletic Association (NCAA) Division 1 runner with a medical history of left high hamstring tendinopathy, oligomenorrhea, osteopenia, and prior metatarsal stress fractures presented with left buttock pain of 4 weeks’ duration. She initially described her pain as tightness after stretching and occasional low back pain without radicular symptoms. Her symptoms were refractory to stretching and electrostimulation. On examination, she reported mild pain with direct palpation in a posteroanterior direction over the anatomical region that included the left lateral sacroiliac joint and left piriformis muscle. She had no pain with palpation over the proximal hamstring or ischial tuberosity. She had full, painless range of motion in both her hips and lumbar spine. Her neurologic examination was normal, including 5/5 motor strength, intact sensation, and 2 reflexes at the patella and Achilles tendon. Piriformis stress tests (a provocative maneuver to stress the piriformis muscle), straight leg raise (a neural tension test), and flexion abduction external rotation (FABER) test (a maneuver that stresses the hip joint and sacroiliac joint) were all negative. Magnetic resonance imaging of the pelvis revealed a stress reaction with marrow edema of the left ileum adjacent to the sacroiliac joint without evidence of cortical discontinuity.