Thumb hypoplasia represents a spectrum of deficiencies from a slightly smaller thumb to a completely absent thumb. The clinical features of a type II hypoplastic thumb include a narrow thumb-index web space, absent thenar muscles, and instability of the thumb metacarpophalangeal joint. This article will focus thumb reconstruction using the ring finger flexor digitorum superficialis to provide opposition and restore metacarpophalangeal joint stability. The technique, postoperative protocol, outcome, and complications will be emphasized.