Cost containment is the major reason for the growth of health maintenance organizations (HMOs) at the end of the 20th century. However, at the turn of the 21st century, whether the HMOs can continue to control costs and to be accepted by providers remains unknown. The purposes of this article are to introduce the trends in HMOs' development and to propose recommendations applicable to health professionals in Taiwan. At the beginning of the 21st century, trends in HMOs' development include (1) discarding the gatekeeper system; (2) increases in the amounts of copayments and deductibles; (3) the end of the contracts between HMOs and providers; (4) the use of fee-for-service to replace capitation; (5) anti-HMO legislation; (6) reductions in the number of HMOss enrollment; (7) outsourcing of HMOs' information systems; (8) increases in the premiums of HMOs; (9) an increase in the number of for-profit HMOs; (10) emphasis on preventive medicine; and (11) HMOs' beginning to earn profits. The capitation and gatekeeper systems adopted by traditional HMOs have gradually been abandoned. HMOs are beginning to shift the responsibility for cost containment from providers to consumers. In addition, HMOs are committed to preventive medicine and the upgrading of their information systems. Although it is difficult to predict the trends in HMOs' development, the experience of the HMOs offers lessons for the health delivery system in Taiwan. It is recommended to reconsider the feasibility of capitation system, to shift the responsibility of cost containment from providers to consumers, to reinforce information systems, and to emphasize quality of medical care in Taiwan.