Many authors have attempted to explain the mechanism of pain in osteoid osteoma and, in the past, several histological studies have been carried out with the specific aim of verifying the existence of nerve fibres within the tumour. The histochemical procedures based on the affinity of nerves for silver stains have made it possible to demonstrate the presence of fine nerve fibres disposed alongside and around the vessels. An analogous study was conducted to confirm this and to supply further morphological and functional information useful for an understanding of the genesis of pain. The study involved three cases of osteoid osteoma using both traditional histochemical procedures and electron microscopy. The latter, in particular, allowed us to confirm the myelinic nature of the nerve fibres observed under optic microscopy. Based on these observations, the authors present a hypothesis on the function of the nerve fibres in the mechanism of pain stimulation.