Alpha interferon has proven efficacy in prolonging remissions in patients with follicular non-Hodgkin lymphoma (NHL) when given concurrently with or after conventional-dose anthracycline-based chemotherapy, but there are limited data on its use after myeloablative conditioning. We prospectively evaluated the toxicity and efficacy of interferon given thrice weekly for up to 5 years post-engraftment in patients with relapsed follicular NHL undergoing autologous stem cell transplant using busulfan-melphalan conditioning. Thirty-seven patients were enrolled in this Australasian Leukaemia Lymphoma Group study and transplanted between 1995 and 1999. Only one patient had received prior rituximab. Two patients died of transplant-related toxicity; 28 of the remainder commenced interferon, but it was discontinued prematurely in most patients due to toxicity (mainly fatigue and depression) or relapse. While the majority of patients (29/36 evaluable: 81 ) achieved a complete remission based on clinical and CT scan criteria post-transplant, most relapsed relatively early, with a median progression-free survival of 2.4 years. The overall survival at 7 years was 49 . Eight patients (22 ), however, remain alive a median of 9.3 years post-transplant, having never relapsed, and another six patients (16 ) remain alive in durable remission after salvage therapy. These results demonstrate that interferon is poorly tolerated post-autograft and hence is unlikely to positively contribute to patient outcome. Long-term follow-up demonstrates that autografting may result in durable remissions in a meaningful minority of patients with relapsed follicular NHL.