This study was conducted to explore treatment and disease-related effects on health-related quality of life (HRQoL) in patients with aggressive lymphoma, to identify predictors for impaired long-term HRQoL, and to analyze the prognostic value of pretreatment HRQoL. Ninety-five patients with aggressive lymphoma, constituting a subset of a randomized multicenter trial comparing CHOP and MACOP-B, entered a HRQoL study, using the EORTC QLQ-C30 questionnaire. Patient scores were compared to scores from an age- and gender-adjusted reference population sample, and evaluation of the prognostic value of pretreatment QoL scores in relation to clinical prognostic factors was performed. Before treatment, patients exhibited lower scores of global QoL, physical, role, and social functions, and more appetite loss, compared to the reference population. Role functioning improved compared to baseline, but remained depressed compared to the reference group more than 8 mo after end of treatment. By then, the patient group displayed no difference in other HRQoL variables compared to that of the reference population. No reliable predictor for impaired long-term HRQoL could be identified. In multivariate analysis, including the factors of the International Prognostic Index, pretreatment global QoL was an independent prognostic marker for overall survival. In conclusion, in this population with aggressive lymphoma and favorable prognostic features, HRQoL was not substantially affected during the first year after diagnosis. Pretreatment global QoL may constitute a significant prognostic factor, meriting further investigation in prospective studies.