Laboratory testing is essential for diagnosis, evaluation, and management. The objective was to describe the type of laboratory events reported in hospitals using a voluntary electronic error reporting system (e-ERS) via a cross-sectional analysis of reported laboratory events from 30 health organizations throughout the United States (January 1, 2000, to December 31, 2005). A total of 37,532 laboratory-related events were reported, accounting for 14.1% of all reported quality events. Preanalytic laboratory events were the most common (81.1%); the top 3 were specimen not labeled (18.7%), specimen mislabeled (16.3%), and improper collection (13.2%). A small number (0.08%) of laboratory events caused permanent harm or death; 8% caused temporary harm. Most laboratory events (55%) did not cause harm. Laboratory errors constitute 1 of 7 quality events. Laboratory errors often are caused by events that precede specimen arrival in the lab and should be preventable with a better labeling processes and education. Most laboratory errors do not lead to patient harm.