Aim of this case report is to present treatment and four-year clinical and radiological follow-up of periapical lesion associated with external root resorption of mandibular molar tooth. 22-year-old male patient was referred from faculty of medicine department of infectious diseases with initial diagnosis as dental abscess originating from left mandibular second molar. The tooth was diagnosed as chronic apical abscess and root canal treatment was initiated. ProRoot Mineral Trioxide Aggregate (MTA) (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA) was applied with MTA carrier and adapted to root canal walls with plugger. Four years follow-up revealed the tooth was asymptomatic and functional, radiography showed healing of periapical lesion and sound periapical structures. MTA is an effective material to seal resorptive cavity and obturate root canals. In cases of severe resorption and related lesions obturation with MTA is a viable option to promote healing and improve treatment outcomes.