Patients with aggressive non-Hodgkin lymphoma (NHL) who relapse after autologous stem cell transplantation (ASCT) have a poor prognosis. Additional therapy is often poorly tolerated, and new treatment modalities are needed. This efficacy and safety study was a retrospective analysis of two phase II trials (NHL-002 and NHL-003) that studied single-agent lenalidomide in patients with relapsed/refractory aggressive NHL with prior (n = 87) compared with no prior ASCT (n = 179). The overall response rate in the ASCT group was 39% [14% complete response (CR)], including 29% in patients with diffuse large B-cell lymphoma, 63% in mantle cell lymphoma, and 60% in transformed lymphoma. The timing of transplant relative to receiving lenalidomide had no effect on outcomes. Median progression-free survival for the ASCT group was 3·7 months (16·9 months for patients in CR; 7·3 months for partial responders) at a median 12·5-month follow-up. Median response duration was 7·9 months. Regardless of prior ASCT, lenalidomide monotherapy was efficacious in heavily pretreated patients with aggressive, relapsed/refractory NHL, with a safety profile that was consistent with prior studies of single-agent lenalidomide.