Background Perianal fistula may affect 15-50% of patients with Crohn's disease (CD). Treatment is complex, requiring a multidisciplinary approach. Darvadstrocel (allogeneic mesenchymal cells obtained from lipoaspirates) was approved in 2018 by the European Medicines Agency and Spanish Agency of Medicines and Medical Products as a treatment for fistulas in CD. Recent European Crohn's and Colitis Organisation (ECCO) andSpanish Working Group on Crohn's Disease and Ulcerative Colitis (GETECCU) guidelines state that darvadstrocel is effective with a favourable safety profile,with a strong level of evidence (level 2).With this study we want to see the real efficacy of darvadstrocel in a Spanish population after 6 months of follow-up.

Methods: The criteria for the Spanish National Health System to fund darvadstrocel treatment are: 1)complex fistula in a patient with CD; 2)failure of conventional and anti-tumour necrosis factor treatment; and 3)absence of collection s>2cm confirmed by pelvic MRI scan at the time of surgery. From November 2019 to April 2022, 73 patients were treated with darvadstrocel at 14Spanish centres and evaluated clinically and radiologically 6 months after treatment.

Inclusion Criteria:

• 1)complex fistula in a patient with CD
• 2)failure of conventional and anti-tumour necrosis factor treatment
• 3)absence of collection s>2cm confirmed by pelvic MRI scan at the time of surgery

Exclusion Criteria:

• Patients with a diagnosis of rectovaginal fistula, rectal stenosis or severe active proctitis were excluded

All patients with complex anorectal fistulas associated with CD treated with darvadstrocel in the 14 dedicated centres from 29 November 2019 to 21 April2022 will be enrolled in the study.