The aim of this study was to determine the clinical outcomes of vascularized hemi-metatarsal composite tissue transfer for the reconstruction of type IIIB hypoplastic thumbs. Twenty-eight patients with type IIIB hypoplastic thumbs treated with vascularized hemi-metatarsal composite tissue transfer were included in this retrospective study with a mean follow-up of 2.4 years. Preoperative digital subtraction angiography was performed to examine the vessel variance. Clinical measures included grip and pinch strength, scar status, and Kapandji thumb opposition score. Subjective Pediatric Outcomes Data Collection Instrument scores and parent satisfaction were also evaluated. Radial arteries were hypoplastic in 82.1% of the cases, and the common palmar digital artery was chosen as the recipient vessel for the tissue transfer. There was no neurovascular complication. The only donor-site complication was a metatarsal fracture that healed with casting. Key pinch and tripod pinch were 29.5% and 45.8% of the normal side, respectively. The mean grip strength was 51.7% of the unaffected side. The mean Kapandji score was 6. The Pediatric Outcomes Data Collection Instrument scores were high for global function; upper extremity function; transfer; and basic mobility, happiness, and comfort. The Vancouver Scar Scale showed an average score of 2.1. All parents were satisfied with the clinical outcomes. Vascularized hemi-metatarsal composite tissue transfer for type IIIB thumb hypoplasia can provide improved subjective outcomes and is a feasible method for the attainment of a five-digit hand. Therapeutic, IV.