This report presents a case in which undiagnosed coronal leakage resul
ted in failure in the endodontic management of a tooth. Coronal leakag
e occurred during root canal treatment as a result of the presence of
deficient composite resin fillings and secondary caries. Despite repea
ted visits of cleaning and dressing, the canal continued to be contami
nated and symptoms persisted. On referral, the reason far treatment fa
ilure was diagnosed. The tooth was successfully treated by the replace
ment of the deficient fillings, after the elimination of underlying ca
ries. Symptoms resolved enabling the completion of the root canal trea
tment.