Strength is regarded as normal in patients with an opposable triphalangeal thumb. Our clinical impression is, however, that intrinsic musculature is probably affected in all forms of triphalangeal thumb. Therefore, we established the strength of 38 thumbs in patients with a triphalangeal thumb. Patients were excluded if the intrinsic musculature was enhanced or if osteotomies of the first metacarpal were performed. On average, strength of all thumb functions was significantly diminished, up to 63% for opposition strength. Strength of the power grip was on average 70%. As shown in this study, strength of the musculature of the thumb is affected in all types of triphalangeal thumb. Although strength of the thumb is diminished, in the investigated group it is apparently sufficient in daily life, as these individuals did not seek surgical enhancement. However, reconstructive procedures that enhance intrinsic musculature must be considered in all types of triphalangeal thumb.