There is evidence that a conservative approach with chemoradiotherapy can achieve long-term local control in patients with anal adenocarcinoma. Identification of suitable patients for this approach remains a problem. We describe a patient with a clinically staged T2N0 tumour, who achieved a complete clinical response on magnetic resonance imaging and positron emission tomography after chemoradiotherapy, but was noted to have residual disease with evidence of lymph node metastasis on pathological examination in the abdominoperineal resection specimen. A complete clinical response does not necessarily equate to pathological response.