Many groups have reported good to excellent clinical outcomes of the Elmslie-Trillat (ET) procedure for recurrent dislocation of the patella. However, the mean follow-up period of these studies was no more than 5 years. We hypothesized that the long-term postoperative outcomes of the modified ET procedure for recurrent dislocation of the patella would be acceptable compared with those of other procedures. The long-term postoperative outcomes of patients treated with the modified ET procedure were examined. A total of 31 knees in 27 patients with recurrent dislocation of the patella who underwent a modified ET procedure (without medial capsular plication) were evaluated. The mean follow-up period was 13.0 years. Pre- and postoperative radiographs were examined to determine the Q-angle, tilting angle, lateral shift ratio, sulcus angle, congruence angle, and Insall-Salvati index. Clinical outcomes were evaluated based on the Fulkerson patellofemoral joint evaluation score, Kujala score, and the presence of the apprehension sign. Radiological evaluation revealed significant postoperative improvements in the Q-angle, tilting angle, lateral shift ratio, congruence angle, Kujala score, and Fulkerson score (p < 0.001). Sixty-eight percent of all patients had a “good” or “excellent” Fulkerson score. The apprehension sign continued to be shown for six knees. Progression of osteoarthritic changes was observed in three knees, and one knee was symptomatic. The modified ET procedure provided satisfactory outcomes based on radiological and clinical evaluations. These results show the long-term effectiveness and safety of the modified ET procedure for recurrent patellar dislocation.