OBJECTIVES: Hyperuricemia (HU) and tumour lysis syndrome (TLS) are important complications leading to increased morbidity and mortality in patients with acute lymphoid or myeloid leukaemia (ALL/AML) and non-Hodgkin lymphoma (NHL). The objective was to calculate incidence and average cost of managing HU and TLS in current daily practice from the payer’s perspective. METHODS: Seven hundred eighty eight patients, both adults and children, from Belgium, Holland, Spain and the UK, who received induction treatment between 1999 and 2000, were screened retrospectively for the occurrence of HU or TLS. In patients fulfilling predefined diagnostic criteria, HU or TLS-related resource use was recorded and costs calculated by applying local unit costs. RESULTS: HU was detected in 18.9% of screened patients, TLS in 5.0% despite 79% prophylaxis. The average cost of HU in the absence of TLS was 672 Euro (SE = 181), of which 218 Euro were for medication and 376 Euro for the hospital stay. The average cost of TLS was 7,342 Euro (SE = 1,412) of which 5,837 Euro related to additional hospitalisation, 719 to interventions (mainly dialysis) and 446 Euro to medication. TLS patients requiring dialysis incurred an average cost of 17,706 Euro compared to 3,887 in non-dialysed TLS cases. Inter-country differences in costs were observed and were solely due to differences in unit costs. Age or underlying malignancy had no significant impact on management costs. CONCLUSIONS: Rates of HU and TLS observed were at the low end of the range compared to previous published reports in specific indications. There is a large variation in costs, and distributions are highly skewed. Patients developing TLS incur 11 times higher costs than patients with HU in whom development of TLS can be prevented. The main cost driver in TLS patients is the need for interventions (dialysis and haemofiltration) that require ICU admission and extra hospital stay.