Trephine biopsy (TB) combined with bone marrow aspiration (BMA) is the most common method for evaluating bone marrow (BM) involvement in non-Hodgkin's lymphomas. Nevertheless, the role of TB in high-grade lymphomas remains controversial. We reviewed the results of 42 consecutive BMAs and TBs performed simultaneously in 29 patients with lymphoblastic lymphoma (LL) and small, non-cleaved cell lymphoma (SNCL). In LL, 8M involvement was documented in 35.4% of the cases by BMA and 22.5% of the cases by TB. In SNCL it was documented in 45.4% of the cases by BMA and 36.3% by TB. There were no statistically significant differences (p > 0.05) in the rates of BM involvement found by TB or BMA in the two types of lymphoma, although BMA appeared to be more sensitive than TB. These observations suggest that routine TB may not be necessary in assessing BM involvement in patients with LL and SNCL.