Congenital lack of elbow flexion results in significant disability and may be seen in conjunction with syndromes, plexopathies, neuromuscular disorders, or as an isolated muscular agenesis of elbow flexors. There are many tendon transfer options to address this issue, but there is a lack of data on the functional results in the pediatric population. In this series, we present 1 patient with isolated muscular agenesis of the biceps and brachialis musculotendinous units and another with this same muscular agenesis in the setting of arthrogryposis. They were treated with anterior ulnar nerve transposition and transfer of the long head of triceps tendon around 2 years of age resulting in functional elbow flexion in both patients.