Lorazepam (Ativan), is a benzodiazepine frequently used to manage anxiety, presurgically, and as a sedative. Common side effects include sedation, dizziness, weakness, unsteadiness, and disorientation. Consequently, lorazepam can have a significant effect on driving ability. We reviewed all positive lorazepam drug-impaired driving cases submitted to the Washington State Toxicology Laboratory between January 1998 and December 2003. The mean concentration found in the blood of these drivers (n = 170) was 0.048 mg/L (std. dev. = 0.06, median = 0.03). Concentrations ranged from < 0.005 to 0.39 mg/L. Eighty-six percent of these drivers tested positive for other drugs in addition to lorazepam that may have contributed to their impairment. There were 23 cases in which lorazepam was the only drug detected. The mean concentration found in the blood of these drivers was 0.051 mg/L (median = 0.03, range < 0.01-0.38). This population was 56% male, with a mean age of 39.5 years, (range 16-72). We obtained Drug Recognition Expert reports containing details of events surrounding arrest and performance on field sobriety tests for 10 of the remaining cases in which no drugs other than lorazepam were present. Lorazepam concentrations in these cases averaged 0.050 mg/L (median = 0.04, range 0.01-0.13 mg/L). This review of these subjects indicates that lorazepam is capable of causing significant impairment to driving and psychomotor abilities, independent of the concentration detected.