Eleven patients with active unicameral bone cysts were treated primarily with placement of demineralized bone matrix in the cyst by using a two-needle technique and a custom large-bore needle. Cyst healing was rated according to the Neer classification, and the average time of healing was 4.5 months. The demineralized bone matrix demonstrated an ability to obliterate the cyst in nine of 11 patients by using a single injection within 4-5 months, and at 2 years' follow-up, no cysts were deemed active or recurrent.