The benefits of partial over radical nephrectomy are well established. The CLOCK trial (CLamp vs. Off Clamp the Kidney during robotic partial nephrectomy) was designed as a multicentre, randomised controlled trial to generate evidence on the role of the off-clamp approach. The study was conducted at seven centres in Italy between September 2015 and November 2018. They included patients with cT1 renal tumours with RENAL score ≤10, normal contralateral kidney and estimated glomerular filtration rate (eGFR) ≥60ml/min/1.73m2. The primary endpoint was absolute variation in eGFR (AV-GFR) at six months. The sample size was calculated based on a superiority trial design assuming there would be no difference between the two groups. Three hundred and twenty-four patients were enrolled and randomly allocated to the on-clamp (160) or the off-clamp (164) arm. Crossover was observed in 14% (23/160) patients in the on-clamp arm and 43% (69/164) patients in the off-clamp arm. On an intention to treat analysis, the six-month median AVGFR was -6.2 (-18 to 0.5) ml/min for the on-clamp group and -5.1 (-14 to 0.1) ml/min for the off-clamp group, with a mean difference between groups of 0.2 (95% CI -3.1 to 3.4; P=0.8). The authors also did a per-protocol analysis with median warm ischaemia time (WIT) of 14.3 (11-18) minutes. The AV-GFR at six months which was -6.8 (-18 to 0.6) ml/min for the on-clamp group vs. -4.2 (-12 to 1.7) ml/min for the off-clamp group, with a mean difference between groups of 1.6 (95% CI -2.3 to 5.5ml/min; P=0.7). This study has shown no difference in functional outcomes which are similar in patients with good renal function exposed to minimal WIT irrespective of the approach. Surgeons with reasonably short WIT should maintain their approach based on this data.