A significant minority of patients with diffuse large B-cell lymphoma (DLBCL) who enter a complete remission following standard first-line immunochemotherapy will relapse. A primary aim of follow-up is to detect early relapse, with the hope of improving outcome following salvage chemotherapy. It is often routine to measure lactate dehydrogenase (LDH) as part of follow-up; however, the evidence for the utility of LDH as a predictor for relapse is scant. A retrospective analysis of the LDH results recorded during the follow-up of 102 patients with DLBCL who achieved a CR following treatment was undertaken in order to determine the utility of LDH as a predictor for relapse (median follow-up 24 months). Despite the fact that the sensitivity of LDH was 69% (95% confidence interval [CI] 39-91), the positive predictive value (PPV) of a raised LDH was only 9/63, 14% (95% CI 6.7-25). Furthermore, in eight of the nine patients who had a raised LDH prior to relapse, symptoms suggestive of relapse were documented simultaneously. As the PPV of a raised LDH is so low and because a raised LDH may cause unnecessary worry, leading to unnecessary radiological investigations, routine evaluation of LDH in patients with DLBCL who achieve CR and who are asymptomatic is not recommended.