Background: Approximately 70 percent of pediatric care occurs in ambulatory settings, yet there has been little research on errors and harm in these settings. Given the importance of understanding harm in ambulatory pediatrics, this study was funded by the Agency for Healthcare Research and Quality (AHRQ) as part of the University of North Carolina (UNC) Center for Education and Research on Therapeutics (CERTs), in partnership with the American Academy of Pediatrics (AAP) Pediatric Research in Office Settings (PROS) Network. Purpose: Learning from Errors in Ambulatory Pediatrics (LEAP) was designed to (1) develop a secure, Web-based tool for reporting errors; (2) identify the types and range of errors; and (3) identify errors that can be generalized across multiple practices. Methods: Data collection was pilot-tested in five pediatric practices in March 2003, using a secure, Web-based tool. After revising the tool, 14 sites collected data from June to September 2003. Three members of the research team (one pediatrician and two patient safety researchers) independently coded the qualitative error reports using the constant comparative method. Reports were coded by medical domain, problem types, and child-specific factors. Coding discrepancies were reconciled by consensus. Results: Study participants reported 136 errors. Data collection via the Web-based tool was very successful; participating practitioners reported a high degree of satisfaction and a minimal number of problems. Errors were reported in several domains: prevention, diagnosis, treatment, patient identification, communication, falls, equipment, and administration. For example, one reported treatment error was “prescription changed from liquid to capsule form of anticonvulsant. Mom misunderstood directions and gave both meds for one week. Child developed blurred vision, stuttering, and ataxia.” Conclusions and implications: Physicians reported errors, yet various members of the care team (parents, nurses, pharmacists) discovered the errors. This suggests that everyone has a role in preventing errors from reaching the child. Information learned from this study will be instrumental in the subsequent design of interventions to reduce errors and improve pediatric patient safety. The success of the Web-based, data collection tool points the way for future online data collection efforts. Further research will clarify the categories of harm observed in ambulatory settings, and explore venues for presenting errors and collaboratively designing and testing solutions.