Following a review of the development of secure units for children, the functioning of the units is assessed with regard to several factors: family background, delinquency history, and characteristics of the children; theories of assessment and treatment; effects of security; interpersonal relations; organization; use of behavioral methods; secure accommodation regulations; and facility function and design. Descriptions are provided of facilities built in the 1960's and 1970's. Building administration and evaluation programs are described; and major problems in the safety, security, and durability of building components and furnishings are outlined. Finally, these child secure units are compared with other secure institutions including regional psychiatric hospitals and post-War prisons. It is concluded that the design of the facilities is a contributing factor in failure of the child secure units to achieve significant general reductions in children's offending after treatment. Moreover, inadequate consideration has been given to minimizing the adverse effects of security, and the small size of units precludes the availability of adequate occupational and recreational programs. List of security equipment manufacturers, 6 tables, and 77 references.