The purpose of the present retrospective study was to analyze treatment choice and outcome in patients with retention/impaction of the mandibular second molar. Radiographic material, from three large clinics, from 106 patients (60 males and 46 females) with 126 retained/impacted permanent mandibular second molars treated during the years 1985–2005 was evaluated for treatment choice and treatment outcome. Follow-up questionnaires were sent to dentists in cases where treatment outcome could not be determined from the radiographic material. Clinical evaluation was not possible as the patients were no longer associated with the clinic where they were treated. The cases were categorized into six groups: (A) no treatment; (B) orthodontic treatment; (C) surgical exposure of the second molar; (D) removal of the third molar; (E) removal of the second molar; and (F) other treatments. The various treatment choices performed during 1985–2005 showed acceptable results in 66 of the cases. In 23 cases, the results were unacceptable. In 37 cases, the radiographic material could not document the outcome nor was evaluation of the final outcome possible due to the patient's young age. Remarkable are the high percentages of unacceptable treatment outcome, 25.9% in group D (removal of third molar) and 23% in group E (removal of second molar). As the material was collected before new advanced methods of surgical uprighting and new methods of orthodontic uprighting had been introduced, these percentages are expectedly lower today. Even so, it is highly recommended to focus especially on these two groups in future studies on treatment outcome.