Meniscus horizontal tears are usually degenerative. It could be asymptomatic and unrelated to knee symptoms. Therefore, there are controversies regarding treatment choices. The aim of this study was to evaluate factors that affect the results of non-surgical and surgical treatments for meniscus horizontal tears. We retrospectively studied 159 patients with meniscus horizontal tears with a minimum 2-year follow-up period. Patients were treated non-surgically or arthroscopically. The treatment results were dichotomized into success and failure. The factors considered were age, sex, joint line tenderness, mechanical symptoms, widest tear gap width on sagittal MRI, cartilage lesion grade, discoid meniscus, tear site, and joint alignment. Joint alignment and cartilage lesion grade were the factors that significantly influenced non-surgical treatment results. The widest tear gap width and cartilage lesion grade significantly affected arthroscopic surgery results. The mechanical symptoms did not show any significant relationship with either treatment result. In treating patients with meniscus horizontal tears, patients with varus alignment and advanced cartilage lesions should be informed of possible poor outcomes with non-surgical treatment. If the patient has a wide tear gap or minimal cartilage lesion, arthroscopic surgery would be a good treatment choice. The mechanical symptom was not an adequate factor for arthroscopic surgery.