Forty children treated with allogenic haematopoietic stem cell transplantation for haematological malignancies, were examined at least 2 years after transplantation. The researchers collected information concerning subjective oral symptoms, the results of a panoramic radiograph and the findings of an oral examination. Nearly all children had tooth development disturbances, including missing teeth, shortened roots, and arrested root development. The study group showed a significantly higher prevalence of missing teeth than the standard values for first and second premolars in both maxilla and mandible, as well as for second molars in the mandible. Children younger than 3 years of age at the start of the treatment missed significantly more teeth than older children. The mean root-crown length ratios of several tooth types were lower when compared with a control group of healthy Finnish children. The mean dental age was higher than the mean chronological age due to early final apical root formation.