Objectives: To investigate the effects of infliximab treatment in patients with complex idiopathic anal fistulas refractory to standard surgical treatment. Materials and methods: We retrospectively evaluated the effects ofinfliximab treatmentin patients with complex idiopathic anal fistulas refractory to standard surgical intervention. The primary outcome was achievement of substantial clinical improvement defined as sustained, reduced inflammatory activity at perioperativeevaluation, i.e., only minimal-to-moderate secretion and induration and a reduction of fistula size of a magnitude that would make it possible to perform a lay-open or sphincter-sparring closure procedure. Secondary outcomes weresymptom improvement, adverse treatment events and fistula healing after the surgical procedure in those achieving the primary outcome. Results: Twenty-two patients were included (18 high transsphincteric, 3complex low transsphincteric, 1 suprasphincteric fistula). Fistulas had been present for a median of 24 [interquartile range, IQR: 12–33] months. In total, 16 patients (73%) achieved the primary outcome of substantial clinical improvement. Median time from infliximab initiation to patients achieved the primary outcome was 11 [IQR: 8–22] months. Sixteen of the patients responding to infliximab received subsequent lay-open or sphincter-sparring closure procedure surgery. Of these, ten (63%) achieved fistula healing. No serious infectious complications to infliximab treatment were seen. One patient developed a new abscess. One patient developed psoriasis (pustolosispalmoplantaris). Conclusions: Infliximab treatment may be considered a supplement to repeated curettage and setondrainage in the management of selected, complex idiopathic anal fistulas. Such combined treatment may make otherwise refractory fistulas amenable to definitive closure attempts.