Bone marrow aspirates (BMA) and trephine biopsies (BMT) are commonly performed in the staging of patients with newly diagnosed Hodgkin's lymphoma (HL) but the value of these procedures is controversial. The purpose of this study was to evaluate the predictive value of the blood count and erythrocyte sedimentation rate (ESR) for bone marrow involvement (BMI) and the influence of BMI on stage and prognostic score. A retrospective analysis of 955 patients with newly diagnosed HL entered into clinical trials in a regional cancer centre between 1975 and 1999 was performed. BMI was identified by BMT in 50 patients (5.2%) but in only five of these by BMA. The negative predictive values of a normal full blood count (FBC) and ESR for absence of BMI were 98.8% and 97.3%, respectively, and the positive predictive value of an abnormal FBC and ESR for presence of BMI were both 6.7%. BMT did not alter initial patient management in a single case but provided valuable prognostic information in certain subgroups of patients. BMA gave no additional staging information over BMT and abnormalities of blood count and ESR were poor predictors of infiltration. We conclude that BMA should be abandoned for staging purposes in HL and BMT restricted to patients with stage IIB or III disease, for whom valuable prognostic information may be obtained.