PURPOSE:A prospective trial was conducted to establish long‐term healing of complex idiopathic anorectal fistula, without extension, after fibrin glue treatment, with clinical assessment and magnetic resonance imaging to determine tract healing.METHODS:Twenty‐two patients undergoing glue instillation after fistula curettage and irrigation were followed up for a median of 14 months. Clinical assessment, short tau inversion recovery sequence magnetic resonance imaging, and combined short tau inversion recovery and dynamic contrast‐enhanced magnetic resonance imaging were performed at a median of three months postoperatively, and their ability to predict outcome in the presence of early skin healing was determined.RESULTS:Of 22 patients, 19 (86.5 percent) had transsphincteric fistulas, 1 (4.5 percent) had a suprasphincteric fistula, 1 (4.5 percent) had an extrasphincteric fistula, and 1 (4.5 percent) had a rectovaginal fistula. None had clinical or radiologic evidence of secondary extension. Despite skin healing in 17 (77 percent) of 22 patients at a median of 14 days after treatment, only 3 (14 percent) remained healed at 16 months. Magnetic resonance imaging with short tau inversion recovery sequences in combination with dynamic contrast‐enhanced magnetic resonance imaging predicted outcome in all 10 assessments (100 percent), compared with short tau inversion recovery sequence alone in 16 (94 percent) of 17 assessments or clinical examination in 12 (71 percent) of 17 (P= 0.02).CONCLUSIONS:The success rate of fibrin glue application for complex anorectal fistulas without extension is 14 percent. Magnetic resonance imaging predicts outcome at an earlier stage than clinical examination.