We reviewed the medical records of 110 consecutive patients at our institution who had acute leukemia and received high-dose cytarabine (Ara-C; HDAC) in order to analyze risk factors associated with HDAC neurotoxicity (NT). There were adequate records on 101 patients who received 147 courses of HDAC. Twenty-six treatment courses (18%) were complicated by NT. The median time of NT onset was 5 days (range, 1 to 10 days), and NT was reversible in 16 of 21 survivors (76%). Patients with severe NT (grades 3 to 4) were less likely to have complete reversal of their neurological deficit than those with mild NT (P less than .1). In our patients, there was no significant association between previously described risk factors (age over 49 years, male gender, CNS disorder, and cumulative HDAC dose greater than 48 g/m2) and incidence of NT. However, treatment courses involving HDAC given during renal insufficiency (serum creatinine greater than or equal to 1.5 mg/dL or an increase in serum creatinine greater than 0.5 mg/dL) were much more likely to be complicated by any degree of NT during administration of HDAC (62%) and severe NT (42%) than those given during normal renal function (8% and 3%, respectively; P less than .001). Of the treatment courses involving patients with estimated creatinine clearances less than 60 mL/min, 76% were complicated by NT compared with 8% of treatment courses involving patients with clearances greater than 60 mL/min (P less than .001). HDAC courses with neurotoxic patients had higher serum creatinines (2.1 +/- 1.4 v 1.1 +/- 0.6 mg/dL), greater increases in serum creatinine (+ 0.5 +/- 0.8 v + 0.07 +/- 0.3 mg/dL), and lower estimated creatinine clearances (61 +/- 35 v 91 +/- 29 mL/min) than those courses with nonneurotoxic patients (P less than .001, all parameters). Patients receiving HDAC during renal insufficiency are at high risk for developing NT. Dose reduction of HDAC should be considered for patients with renal insufficiency.