Data on relapsed primary central nervous system lymphoma (PCNSL) are limited. We have evaluated the clinical characteristics and outcome of relapsed PCNSL patients from two German trials. Patients with relapsed disease after primary treatment were studied. Primary therapy consisted of high-dose methotrexate-based chemotherapy in all patients. Treatment for relapse was not predetermined. After a median follow-up of 22.5 months, 52 (36%) patients with relapse were identified among 143 patients with complete remission (CR) after primary treatment. The median disease-free survival was 10.25 (3-47.5) months. The median age at relapse was 59 years. Forty-four of 51 evaluable patients relapsed within the CNS, 6 systemically and one both cerebrally and systemically. The median survival time after first relapse was 4.5 (0.5-40.5) months. Karnofsky performance status (KPS) at relapse (P = 0.004), site of relapse (isolated systemic versus other, P = 0.049) and treatment for relapse (versus no treatment, P = 0.001) were independent prognostic factors for survival after relapse in multivariate analysis. Survival of patients with relapsed PCNSL is poor despite high response rates to salvage therapy. Good KPS, isolated systemic relapse and treatment for relapse were significantly associated with longer survival.