Oral mucositis (OM) is a common side effect experienced during haematopoietic SCT (HSCT), and it can have a significant impact on the quality of life of patients. A descriptive nurse-led study was undertaken in 19-member centres of the Italian national transplant group (GITMO) evaluating incidence, severity and duration of OM in patients undergoing HSCT. Data from 1841 patients between 2002 and 2006 was analyzed. Initial medical history and oral cavity assessment was performed. Assessment was repeated on the day of transplant, then daily, using the WHO (World Health Organisation) oral toxicity scale. A total of 71% of the patients evaluated developed mucositis and 21.6% developed severe mucositis. Duration of OM in most cases lasted for 10-14 days and resolved along with marrow reconstitution. Oral mucostitis is a frequent side effect in patients undergoing HSCT. The onset of severe mucositis seems to be related to the conditioning regimen used. This database provides a descriptive overview of the incidence and severity of mucositis and has encouraged participating centres to adopt routine evaluation and measurement of the oral cavity. The assessment tools are still used in some centres, providing a basis for further collaborative research projects.