OBJECTIVE: To assess the effectiveness of ultrasonography for determining which pediatric midline neck masses should be treated surgically. DESIGN: Retrospective study. SETTING: Tertiary care pediatric hospital. PATIENTS: Pediatric patients with a midline neck mass who underwent ultrasonography from 2003 to 2011. MAIN OUTCOME MEASURES: Demographics, ultrasonography, and surgical and pathology reports were studied. The ultrasonography findings and pathological analyses were compared. RESULTS: One hundred twenty-two patients met the inclusion criteria. The most common diagnosis obtained by ultrasonography was thyroglossal duct cyst (48.4%), followed by reactive lymph node (27.9%). Ninety-five of 122 patients (77.9%) underwent surgery. Twenty-seven patients (22.1%) were treated nonsurgically. The diagnosis and characteristics obtained from ultrasonography were confirmed by surgical pathologic analysis in 84.2% of the surgical cases. Of the 95 patients who underwent surgery, 85 (89.5%) had a non-lymph node lesion diagnosed by ultrasonography and confirmed by pathologic analysis. Ultrasonography was only 66.1% accurate in specifically diagnosing thyroglossal duct cyst and 30.0% accurate in specifically diagnosing reactive lymph node when compared with surgical specimens. CONCLUSIONS: Ultrasonography is helpful in determining the pediatric midline neck masses that need to be removed surgically. It is less helpful in determining the exact pathologic characteristics of the lesion.