This case report highlights the importance of using a dental operating microscope (DOM) and ultrasonic endodontic tips (UETs) to locate all root canals in the lower first premolar. A 53-year-old woman presented to our clinic with pain in the lower right first premolar. After a detailed search using a DOM and UETs, three root canals were found, prepared with rotary HyFlex endodontic files, and obturated using the lateral condensation technique. At the five-year follow-up after treatment, the tooth was completely restored and fulfilling its function, with no signs or symptoms of any post-treatment flare-up.