The HARP study aims to observe the long-term clinical course of anxiety disorders and assess how comorbid psychiatric conditions influence recovery or recurrence. Participants were recruited and underwent baseline assessments in 1989 to 1991 after being referred from 11 clinical treatment facilities across the New England area of the United States of America. At baseline, there were 711 participants aged 18 to 86. Follow-up interviews were conducted at 6-month intervals for the first two years, annually for years 3-6, and then every 6 months from years 7 to 12. An associated study, Harvard/Brown Anxiety Research Project - Phase II (HARP-II), has similar aims but has recruited a new cohort of African American, Latino, and Non-Latino White participants.