A prospective clinical and microbiological surveillance study was conducted during a 26-month period to evaluate consecutive malignancy or post-bone marrow transplant patients with positive blood cultures. The study included 859 episodes of bloodstream infection (BSI) in 719 patients. There were 6.9 BSI episodes/1000 patient-days. Overall mortality was 25%. The median age of patients was 43 years, with 71% of episodes occurring in patients aged > 18 years. Patients with underlying haematology malignancies accounted for 38.2% of the episodes. An indwelling central vein catheter was present in 61% of episodes. BSI origin was unknown in 27% of episodes, associated with other sites in 49.6%, and catheter-related in 23.4%. There were 638 concomitant infection sites, of which the most common were pulmonary (28.4%), urinary tract (14.8%), and non-surgical skin or soft tissue (9.7%). In total, 1039 microorganisms were isolated within 48 h of the first blood culture, of which Gram-negative bacilli accounted for 56%. Among Klebsiella pneumoniae and Escherichia coli isolates, 37.8% and 8.9%, respectively, produced extended-spectrum beta-lactamases. High rates of ceftazidime resistance were detected among Acinetobacter spp. (40%) and Enterobacter spp. (51.2%). E. coli and K. pneumoniae were isolated frequently from haematology patients, and Enterobacter spp. from solid tumour patients. E. coli, K. pneumoniae and Pseudomonas aeruginosa were isolated more often from neutropenic than from non-neutropenic patients. Oxacillin resistance was detected in 18.7% of Staphylococcus aureus isolates. It was concluded that continuous multidisciplinary surveillance of BSI is warranted in this high-risk group of patients in order to develop strategies for antimicrobial resistance control and treatment of infectious complications.