Onychomadesis usually arises from an inflammation of the paronychium or as a result of blisters and hemorrhaging under a nail that has been struck or compressed. No documented interactions between basic fibroblast growth factor (bFGF) and onychomadesis have hitherto been reported. This case report describes a 25-year-old woman with onychomadesis following infection of the ingrown nail of her left thumb. After ten months of observation with no treatment showed no regrowth of her left thumbnail, the external use of bFGF and antibiotic ointment was started. One month later, nail regrowth was observed up to the halfway point of the nail bed, and after treatment for three months, the regrown nail reached the top of the nail bed. Both thumbnails now looked identical. This case suggests that external use of bFGF can promote nail regrowth in cases of onychomadesis with delayed regrowth of the nail.