Patients with diffuse large B-cell lymphoma (DLBCL) who fail to complete planned treatment with R-CHOP due to toxicity are sparsely described. We investigated the extent of failure to complete treatment (6 cycles or more, or 3 cycles + RT for patients with stage I disease) with R-CHOP for reasons unrelated to non-response, the determinants of such failure and the outcome among these patients.3149 adult DLBCL patients who started primary treatment with R-CHOP were identified through the Swedish lymphoma register 2007-2014. Of these, 147 (5%) stopped prematurely after 1-3 cycles of R-CHOP for reasons unrelated to non-response, 168 (5%) after 4-5 cycles and 2639 patients (84%) completed planned treatment. Additionally, 195 (6%) patients did not complete treatment due to non-response or death before treatment end. In a multivariable logistic regression model, age >75 years, poor performance status, extranodal disease and Charlson Comorbidity Index ≥1 were significantly associated with failure to complete planned R-CHOP treatment for other reasons than non-response. Non-completion of treatment strongly correlated with survival. Five-year overall survival for patients who received 1-3 cycles was 26% (95% CI: 19-33%), 49% (95% CI: 41-57%) for 4-5 cycles and 76% (74-77%) for patients who completed treatment.Failure to complete planned R-CHOP treatment is an important clinical issue associated with inferior survival. Old age and poor performance status most strongly predict such failure. These results indicate a need for improved treatment tailoring for patients with certain baseline demographics to improve tolerability and chance for treatment completion. This article is protected by copyright. All rights reserved.