Objective: To determine the frequency of factors associated with habitual abortion in 198 Korean couples. Methods: A total of 198 cases at the department of Obstetrics and Gynecology, Asan Medical Center, Korea from July 1989 to December 2001 that were diagnosed as habitual abortions were included in this study. The cases were divided into 2 main groups; a primary habitual abortion group and a secondary habitual abortion group. They were classified according to etiology. Results: The number of primary habitual abortion cases was 157 (79.3%) and that of secondary habitual abortion cases was 41 (20.7%). The mean age and number of previous abortions were not different between the two groups. The etiologic factors of the primary habitual abortions were anatomical (31.8%, 42/132), immunologic (24.2%, 32/132), unexplained (23.5%, 31/132), endocrinologic (15.2%, 20/132), genetic (12.9%, 17/132), and infection (1.5%, 2/132). The factors of the secondary habitual abortions were immunologic (36.8%, 14/38), unexplained (28.9%, 11/38), anatomical (21.1%, 8/38) and endocrinologic (13.2%, 5/38). The successful pregnancy rate following secondary habitual abortion was 42.0% (17/38), significantly higher than that following primary habitual abortion which was 34.8% (50/132) (p-value