The genioglossus muscle was detached from the mandibular mental spines in seven patients with anterior open bites and obvious tongue-thrust habits. Maximum protrusive tongue forces were measured on a zero-to-ten scale before and after surgery. The average presurgical recording of 4.83 was reduced to 2.67 postoperatively; however, the six-month average measurement was 3.22, a figure approaching the original average. Comparisons were also made between cephalometric records and plaster models taken before and six months after the operation. The surgical procedure significantly reduced tongue forces; the usefulness of the operation in conjunction with orthodontic treatment should be explored.