In diffuse large B-cell lymphoma (DLBCL), previous studies have suggested that, while concordant bone marrow (BM) involvement confers a poor prognosis, discordant BM involvement does not. Whether this correlation is independent of the non-Hodgkin lymphoma International Prognostic Index (IPI) was previously unknown. We reviewed all DLBCL case histories from 1986 to 1997 at our center with complete staging, IPI data, and follow-up. A total of 55 (11.2%) of 489 patients had BM involvement, including 29 with concordant involvement and 26 with discordant involvement. The 55 patients with BM involvement had a poor prognosis compared with the uninvolved BM group (5-year overall survival [OS], 34.5% versus 46.9%; log-rank P = .019). However, concordant involvement portended a very poor prognosis (5-year OS, 10.3%; P < .001), whereas discordant involvement did not (5-year OS, 61.5%, P value nonsignificant). Compared with the discordant subset, the concordant subset patients were older, had a higher serum lactate dehydrogenase level, and a significantly higher IPI. However, the poor survival associated with concordant BM involvement was independent of the IPI score (P = .002, Cox regression). We conclude that in patients with DLBCL, concordant but not discordant BM involvement confers a very poor clinical outcome. Furthermore, concordant BM involvement is an independent adverse prognostic factor.