This study was undertaken to explore the antecedent factors and process of the treatment-seeking behaviors of medical and alternative treatments in patients with arthritis using methodological triangulation. The data were collected from 995 arthritic patients who were registered either in a center of rheumatology for medical treatment or residents of community having no treatment to classify different treatment patterns. Sixteen patients with various types of treatment only, alternative treatment only, and no treatment were selected among the total samples to identify the antecedent factors through in-depth interview. The quantitative data were analyzed by percentile, t-test, chi-square test and discrimant analysis using SAS PC program, while the qualitative data were analyzed by means of grounded theory methodology. Treatment-seeking behaviors of patients change from the early stage to the sick-role stage. At the early stage, initial characteristics of pain and acculturation of medical professionalism affect the choice of treatment patterns. The acculturation of medical professionalism is affected by health care accessibility, level of education, duration of sickness and lay referral system. At the sick-role stage, lay referral system and acculturation of medical professionalism affect the choice of treatment patterns. The acculturation of medical professionalism is affected by characteristics of symtoms, perceived treatment effects, perceived causes of diseases and socio-economic status as well as health care accessibility, level of education and lay referral system. In conclusion, different factors as well as common factors are influencing the treatment-seeking behaviors depending on the disease and treatment stages. More detailed further studies are required to explore the value system or medical acculturation of patients which is one of the most important factors in decision-making about treatment modalities.