The complications associated with the use of Ommaya reservoirs in 106 patients with meningeal involvement due to malignant disease are reviewed. Twenty-seven patients had acute lymphoblastic leukemia, 12 acute myelogenous leukemia, 3 chronic lymphocytic leukemia, 34 lymphoma, 29 carcinoma, and 1 chronic myelocytic leukemia. There were 11 technical complications, including 1 death due to misplacement of the catheter, 2 mild intraventricular hemmorrhages, and 5 malfunctioning reservoirs; 3 required craniotomies (1 for subdural hematoma and 2 for subdural hygroma); 13 cases of bacterial meningitis occurred in 10 patients. One patient died of Staphylococcus aureus meningitis. The organisms causing the other infections were mainly coagulase-negative staphylococci (8 cases) or Propionibacterium acnes (2 cases). The projected infection rate for all patients (by Kaplan-Meier analysis) during the first year following insertion of a reservoir was 15%. Successful use of Ommaya reservoirs requires expert surgical implantation and meticulous care during accessing to minimize complications.