ObjectiveTo compare the mid-term effectiveness of arthroscopy versus conservative treatment on symptomatic discoid lateral meniscus (SDLM) in middle-aged and elderly patients. Methods The clinical data of 118 middle-aged and elderly patients (154 knees) with SDLM who received arthroscopy or conservative treatment between June 2014 and May 2016 were retrospectively analyzed, including 76 patients (96 knees) in the arthroscopy group (group A) and 42 patients (58 knees) in the conservative treatment group (group B). There was no significant difference in age, gender, and body mass index between the two groups (P>0.05). Compared with group B, the symptoms duration in group A was longer, the incidences of discoid lateral meniscus injury and mechanical symptoms were higher, and the visual analogue scale (VAS) score and Lysholm score before treatment were worse, with significant differences (P<0.05). VAS score and Lysholm score before and after treatment were recorded and compared. ResultsThe patients in both groups were followed up 60-74 months, with an average of 66.3 months. The follow-up time of group A and group B was (65.9±3.5) months and (67.0±4.0) months respectively, with no significant difference (t=–1.615, P=0.109). At last follow-up, in either group A or group B, the VAS score and Lysholm score significantly improved when compared with those before treatment (P<0.05). The differences of VAS score and Lysholm score in group A before and after treatment were significantly better than those in group B (P<0.05). ConclusionArthroscopy and conservative treatment have a satisfactory mid-term effectiveness on SDLM in middle-aged and elderly patients. However, the improvement of symptoms and function of arthroscopy was significantly better than that of conservative treatment. For middle-aged and elderly SDLM patients with invalidated conventional treatment for 6 months, severe clinical symptoms, long duration of symptoms, and combined with mechanical symptoms, arthroscopy should be given priority even if they are complicated with early osteoarthritis.