Seemingly spontaneous subcutaneous ruptures of the flexor tendons of the hand are not frequently encountered. The case studied is that of a young man whose deep flexor tendon of the third finger snapped during a slight effort. The histological and immunohistochemical analysis led to the conclusion that there was localization of an intra-tendinous neurofibroma, which would seem to be a so-far undescribed phenomenon. The patient presented neurofibromas elsewhere and had pigmented spots on the body, which enabled Von Recklinghausen's disease to be diagnosed.