We read with interest ‘Resuming elective operations after COVID-19 pandemic’. National Institute for Health and Care Excellence guidelines recommend strict social distancing for 14 days before the procedure, and self-isolation during the 3 days from a preoperative SARS-CoV-2 test to the date of operation.We report a case of a 76-year-old man admitted for an elective laparoscopic anterior resection for colorectal cancer that had been postponed owing to the pandemic. A preoperative SARS-CoV-2 swab was positive, which delayed his operation by a further 14 days before a repeated swab that returned a negative result. The patient remained asymptomatic throughout. Despite an uncomplicated operation, the patient was noted to be persistently febrile with no other symptoms on day 2 after the procedure, at which point a third SARS-CoV-2 swab was performed and was positive. CT of the chest, abdomen, and pelvis showed no evidence of postoperative complications and no signs of COVID-19, but did find a small pulmonary embolism for which the patient was started on anticoagulation.This case highlights the dubious relevance of preoperative SARS-CoV-2 tests. The patient’s second swab may have been a false-negative (estimated rate 30–50 per cent). It is arguable whether his second positive swab had a significant effect on prognosis as the patient was discharged on postoperative day 4 and has recovered well at home. Early studies suggested that 20 per cent of individuals can have a positive COVID-19 result for 1 month after symptom onset. The risk of hospital-acquired COVID-19 remains a possibility in this instance, with estimates as high as 16.2 per cent.As hospitals struggle with the ever-increasing backlog of cases, we are clearly in need of a more robust method of preoperative COVID-19 risk assessment, given the questionable validity of a swab result. The impact on both cancer and non-cancer surgery from delayed return to full capacity is yet to be determined.Disclosure: The authors declare no conflict of interest.