Our aim was to evaluate the long-term treatment outcome of a systematically applied orthodontic screening and early treatment strategy in a public dental health care system, with special reference to occlusal stability at least 5 years post-retention. The subjects (N = 68) belonged to one age cohort born in a Finnish rural municipality (N = 85), and they were regularly followed from 8 to 20 years. Persons with malocclusions were screened and treated according to pre-planned protocol. Treatment need was assessed according to the Dental Health Component of the Index of Orthodontic Treatment Need, and treatment outcome using the peer assessment rating (PAR) Index and Little’s Index of Irregularity. Eighty-two per cent of the treated participants were out of retention (mean 6.9 years post-retention) at age 20. Definite treatment need in the study population decreased from 37% to 3 %. In the treated group, the mean PAR improvement decreased from 65 % to 63% from age 15 to 20 years. The mean irregularity score for the mandibular incisors was 4.0 [standard deviation (SD) 2.4] and for maxillary incisors 3.7 (SD 2.1) with no significant difference between treated and not treated subjects. The results suggest that definite need for orthodontic treatment may be predominantly eliminated from the target population with a systematically implemented treatment strategy focusing on early treatment with simple appliances. Emphasis on early timing of treatments may have contributed to the good long-term stability of treatment results.