In patients with neoplastic meningitis (NM), the rapid institution of intrathecal therapy may ameliorate the course of disease, indicating that a timely diagnosis is clinically relevant. As immunocytology (IC) of cerebrospinal fluid and magnetic resonance imaging (MRI), as diagnostic methods, have potential pitfalls, the present study assessed the results of both methods, to determine the predictive capability of the initial evaluations with respect to the risk that the patient would develop NM during the course of their disease. A total of 166 individuals with B-cell non-Hodgkin's lymphoma (B-NHL; n = 95), B-acute lymphocytic leukaemia (ALL; n = 18), acute myeloid leukaemia (n = 27) or solid tumours (n = 26), with at least one definitive IC and MRI result within 3 weeks, were evaluated at a median follow-up of 29.5 months (range 6-53 months). IC and MRI results reached the highest concordance (98%) in B-NHL patients and were most discordant in ALL patients (43%). In haematological malignancies, IC displayed considerable sensitivity, ranging from 89% to 95%, while MRI had very low sensitivity. Conversely, MRI showed high sensitivity (100%) and specificity (92%) in solid tumours. We conclude that IC is of particular value in the diagnosis of NM due to haematological malignancies while MRI is superior to IC in the diagnosis of NM due to solid tumours.