Aim: To describe unusual variations in the root morphology and root canal systems of a first maxillary molar retreated for pain and prosthetic reasons. Summary: Normally maxillary first molar teeth have three single roots and almost always have four canals. A 46-year-old patient presented for non-surgical retreatment prior to undergoing prosthetics. The maxillary first molar exhibited three distinct root canals in the mesiobuccal root canal system. The incidence of three canals in the mesiobuccal root canal is very rare. However, this anatomical deviation may present an unfavourable outcome if clinicians fail to recognise the difficulties. Conclusions: Root morphology may present a challenge for clinicians during root canal treatment. Thorough clinical and radiographic interpretation is important in recognising anomalous root and root canal systems. Finally, successful root canal treatment requires an accurate diagnosis of the root canal system using available aids. Schlagwörter: first molar, retreatment, unusual anatomy