Celecoxib, a cyclooxygenase-2 inhibitor, was effective in treating intractable long-lasting LM in a girl, thus preventing life-threatening airway compression. Lymphatic malformation (LM) is a congenital disorder resulting from an abnormal development of lymphatic vessels. LM may result in problems of cosmesis and functional impairment, including airway compression. An 11-year-old girl was referred to our department with increasing dysphagia caused by a large left cervical LM with a long history of treatment. Because of the LM location, surgical resection was not an option, and various therapies, including use of picibanil, had proven ineffective. Celecoxib treatment (100 mg/day) was initiated for local pain management. Softening of the lesion was observed 2 weeks after treatment initiation, and the dose was increased to 200 mg/day with additional shrinking of the LM over the next 2 weeks. With parental consent, celecoxib was continued, with a 65% reduction in volume achieved at 6 months. The patient discontinued treatment at 12 months, and the LM volume increased. Control over the LM was achieved with resumption of celecoxib treatment. After 2 years of treatment, the LM persists, but the size of the malformation is significantly smaller. No adverse effects of celecoxib treatment were observed. The anti-cyclooxygenase-2 effect of celecoxib prevented lymphatic vessel growth through an inhibition of cyclooxygenase-2 activity in the conversion of prostaglandin to prostaglandin E2. In conclusion, celecoxib may be a promising therapeutic agent for LM management.