Purpose Patients with cancer are not always treated according to available guidelines. Factors such as age and comorbidities are frequently used as arguments for nonadherence. The aim of this study was to measure guideline adherence with guideline-based indicators for patients with non-Hodgkin's lymphoma (NHL) and to examine the need for improvement, considering relevant arguments. Methods A RAND-modified Delphi procedure was used to systematically develop NHL indicators. We evaluated their improvement potential (defined as <90% score) in a random sample of patients with NHL (N = 431) diagnosed in 2006-2007 in 22 hospitals in the Netherlands with data from medical records. Multilevel logistic regression analyses were used to estimate the relationship between indicator scores and factors: comorbidity index (combined with age), stage, patient's objections, and lymphoma type. Scores were adjusted for significant factors. Results Of the 20 indicators developed, 16 had improvement potential. Scores were lowest for assessment of International Prognostic Index, 21%; imaging of neck, thorax, and abdomen and bone marrow examination during the diagnostic process, 23%, and after chemotherapy, 37%; adequate pathology reporting, 11%; and multidisciplinary discussion of patients, 21%. Scores for eight indicators were better for patients with a low Charlson index, stage III or IV disease, no objections to care, and aggressive lymphoma. After adjustments, adherence to all but one indicator (administration of the combination of rituximab and cyclophosphamide-doxorubicin-vincristine-prednisone) remained <90%. Conclusion In the Netherlands, almost all indicators for NHL needed improvement. This should be evaluated in other countries as well. International efforts should be undertaken to improve the quality of care of this often curable malignancy. J Clin Oncol 29: 1436- 1444.