In Finland, adults born in 1961 or later were progressively entitled to subsidies for dental care from private practitioners during 1986-90, while at the same time having access to care in the Public Dental Service. The aim of this study was to compare the effects of attendance frequency of private dental care on treatment costs and treatment spectrum for the heaviest and lowest users over a period. Three separate cohorts of recipients of reimbursements were formed, using the Social Insurance Register. The highest and lowest cost groups in 1986, 1990, and 1994 were followed up to 1997. Initially, the mean numbers of visits were 1.2-1.3 and 5.2-5.6 and cost Euro 48 53 and Euro 358-379 among low users and heavy users, respectively, in all cohorts. Among the heavy users (the high-cost category) infrequent attendance was related to higher and frequent attendance to lower mean annual costs of care. Among the low users (the low-cost category the opposite was true. Those who initially belonged to the high-cost category received in 1997 significantly more (P