Stem cell therapy in dogs has increased considerably in recent years; however, there are few publications on the treatment of perianal fistulas (PF) in this species. The aim of this open-label clinical trial was to demonstrate the efficacy and safety of a new protocol for the in situ administration of low-dose adipose-derived allogeneic stem cells (ASCs) for the treatment of refractory spontaneous perianal fistula. The methodology consisted of applying one to three doses of 5 × 106 cryopreserved allogeneic ASCs to each fistula. The study was performed in 14 dogs regardless of sex, breed, or age, with a clinical diagnosis of refractory PF. Cells diluted in phosphate-buffered saline were applied to five sites of the PF in an amount of 1 × 106 per application site. Efficacy was determined by the complete closure of the fistula, which was observed in 100% of the cases studied one month aft...