The National Cancer Research Network (NCRN) is currently coordinating a Phase III randomised study (LY05) comparing fludarabine and cyclophosphamide (FC) with or without rituximab (R) for previously untreated mantle cell lymphoma (MCL). The combination of FC is well-recognised as significantly immunosuppressive and there are concerns that adding rituximab may increase infection risk further. The impact of rituximab on other markers of toxicity is also unclear. We analysed the toxicity data on 139 patients treated within the NCRN LY05 trial. Non-hematological toxicity was similar between the two treatment arms. The only difference in hematological toxicity was a higher rate of lymphocytopenia with fludarabine cyclophosphamide and rituximab (FCR), which did not translate into increased febrile episodes or infections. In conclusion, the addition of rituximab to FC for previously untreated MCL has no significant impact on toxicity.