this retrospective study aims to analyze the usefulness of bilateral bone marrow biopsy in bone marrow infiltration by diffuse large b-cell lymphoma (dlbcl). our objectives were to assess the incidence of unilateral bm involvement by dlbcl and compare fragment length obtained from positive and negative samples for infiltration. furthermore, we compared the differences between unilateral and bilateral infiltration correlating with lactic dehydrogenase (ldh) and computerized tomography (ct) staging. we evaluated 268 cases of dlbcl and observed medullary infiltration in 34 cases (13%). it was not possible to evaluate 6 out of 34 cases. 70 bm fragments were reviewed as to the presence or absence of infiltration and length. the mean number of fragments per case was 2.5; the mean bm fragment length was 11.01 mm (± 5.12 mm) and the mean bm fragment length per case was 27.53 mm. there was unilateral bm infiltration in six cases (21.4%). there were no differences in the mean fragment length as to the presence/absence of infiltration 10.95 mm (± 5.2 mm) versus 11.57 mm, p > 0.05, respectively. there were no differences in 23 cases between the comparison of unilateral medullary infiltration versus bilateral with lactic dehydrogenase and ct staging. we concluded that bilateral bone marrow biopsy was superior to unilateral because it may increase by 21.4% the detection of bm involvement by dlbcl.