Abstract: A method and system for grouping medical claims data, including outpatient medical claims, into medical events for further analysis is disclosed. Historical outpatient medical claims data is first aggregated by one or more categorization schemes, and then grouped by patient and date. Once the outpatient medical claims data is aggregated and grouped, the methods disclosed build outpatient events by further grouping together disparate medical claims data records that represent a single encounter with an outpatient healthcare system. The outpatient events may be used for analyzing aspects of outpatient care.