Background <p>Dysplasia Epiphysealis Hemimelica (DEH), or Trevor’s disease, is a rare developmental disorder characterized by abnormal cartilaginous overgrowth in the epiphyses of long bones. The condition predominantly affects children, with an estimated incidence of 1 in a million, showing a male-to-female ratio of 3:1. Typically, it involves the lower limbs, especially the ankle, and presents between ages 2 to 14. The etiology remains unknown. First described by Mouchet and Berlot in 1926, the disease has since undergone multiple nomenclatures and classification updates. Though common in the lower limbs, involvement of the sacroiliac (SI) joint is extremely rare, with only two reported cases.</p> Case presentation <p>We report a 15-year-old female presenting with a one-year history of pain in her elbows, knees, hands, and back, with accompanying morning stiffness. Imaging revealed an abnormal articular surface in the right SI joint and focal thickening of the ilium, with mild sacral sclerosis but no signs of malignancy. The diagnosis of Trevor’s disease affecting the SI joint was confirmed based on imaging. The patient was managed conservatively with non-steroidal anti-inflammatory drugs and physical therapy.</p> Conclusions <p>DEH is a rare, developmental skeletal disorder that can present with symptoms resembling other conditions, such as sacroiliitis. Our patient, diagnosed with DEH, is currently managed conservatively with NSAIDs and physical therapy, showing stable symptoms. Regular monitoring is crucial to detect any potential lesion growth or joint deformities. No malignant transformation has been reported, but ongoing follow-up is important to ensure effective management of this rare disorder. Early recognition of DEH can help differentiate it from other conditions with similar presentations.</p>