Taurodontism occurs either as an isolated, singular trait or in association with syndromes and with some ectodermal anomalies. Successful endodontic treatment of taurodontism has rarely been reported. This article describes the successful treatment of a case of taurodontism with 5 canals. In addition, with the suggestion of taurodontism, as well as the clinical features of the patient, a tentative diagnosis of Klinefelter's syndrome was made. This diagnosis was proven after a chromosomal study. The discovery of taurodontism should alert the dentist that there may be associated systemic problems.