Objectives: Oral mucositis and their correlation with oral infections, pro-inflammation agents and deficiency of proteins such as mannose binding lectin in haematopoietic stem cell transplantation (HSCT) have been part of an ongoing study at the Haematology and Oncology, Queen Mary Hospital in Hong Kong. Methods: A cohort of randomly selected adult patients with hematological disorders who underwent HSCT during 2005-07 was screened from the day of admission until discharged. Confounding variables include the type of donor, conditioning regimens, immunosuppressants and opioid analgesics used, disease state, hematological values and, febrile episodes. Oral mucositis scoring system (OMS) was adopted with modifications (WHO). The assessment and sampling of specimens was conducted by dental specialists and/or transplantation specialty nurses. Inter-examiner cross validations were done prior to actual assessment period. Mouth mirrors and bedside lighting were used to evaluate the oral conditions. Results: A total of 65 adult patients were participated in this study. They included 39 males and 26 females with an age range of 17-65 years with diseases such as myeloma, lymphomas, acute leukaemia and, pre-leukaemia. Forty-eight (74%) had chemotherapy alone and 17 (26%) had combined chemotherapy and radiation as conditioning regimen. Donors included autologus (20, 30.7%), allogenic (16, 24.6%) and syngenic/sibling match (29, 44.6%). The total OMS ranged between 10 and 25 (normal total score = 9) with no significant difference between the variable scores amongst autologus, allogenic and sibling-match. Hospital stay was highest in the allogenic group (mean, 35 days) compared with sibling-match (mean, 30 days) and autologus (mean, 25 days). OMS correlated well with neutropenia (p=0.0004), high pain score (p=0.005) and thrombocytopenia (p<0.0001; ANOVA). Conclusions: OMS significantly correlated with the causative events of oral complications such as neutropenia and thrombocytopenia and positively correlated with pain visual analogous score. Type of donor cells was correlated well with duration of hospital stay.