Anorectal adenocarcinoma is a very rare complication which can occur during the long-lasting evolution of perianal fistulas (PAF), chronic inflammation being the main predisposing factor incriminated for malignant evolution. Moreover, in rare cases (only 28 being published until now), adenocarcinoma developing at the level of a perianal fistula may occur by migration of tumoral cells originating from a rectal cancer into the granulation tissue of the fistula. We present the case of a patient with a rectal adenocarcinoma that has metastasized to a perianal fistula, in evolution for 7 years. Clinical suspicion of malignant seeding at the site of the fistula has been confirmed by immunohistochemical studies.