Muscle hernias result from the protrusion of muscle through acquired or congenital fascial defects. They most often occur in the lower extremities of young adults, typically men. There has been limited description in the literature of this entity in children. Our purpose is to evaluate the demographics, presentation and imaging findings of muscle hernias diagnosed by US in our pediatric patient population. We conducted a retrospective review of all lower extremity muscle hernias diagnosed by US in patients younger than 19 years of age, from January 2001 to March 2011, evaluating the reason for referral, imaging performed before and after US, and subsequent clinical course. Sixteen children were diagnosed with muscle hernia by US, 11 girls and 5 boys, ages 3 to 18 years (mean 13.8). Sixty-nine percent (n = 11) involved the tibialis anterior. Clinical suspicion for muscle hernia was present in seven patients (44%). Of the four cases where MR was performed before US, three were interpreted as normal. In 13 cases (81%), the radiologist reported that dynamic imaging with provocative maneuvers (plantar flexion, standing, squatting) was either necessary or helpful in visualizing the muscle hernia. Four children had surgery to treat symptoms. Muscle hernias are often not suspected clinically in children. US with dynamic imaging and provocative maneuvers is key to diagnosis. US confirmation of a muscle hernia provides a reassuring diagnosis and helps exclude the presence of an aggressive lesion. Surgical intervention is an option for persistent symptoms, but is often not necessary.