Non-identifying information may be revealed by the agency or the court upon written request by adoptive parents, or adopted adult.

Missouri law provides that adult adoptees (age 21) may petition the court to receive information about their birth parent(s).

If the adoption was instituted prior to August 13, 1986, the court must order court personnel or a child-placing agency to contact the adoptee's adoptive parents. The court personnel or agency may not contact the birth parent(s) without the written permission of the adoptive parents. If the adoptive parents provide such permission, the agency or court personnel must attempt to contact the birth parent(s). Court personnel have three months to conduct such a search. If a birth parent is contacted, he or she may file a consent to the release of identifying information.

If a consent is not filed or the agency or court personnel are unable to notify the birth parent, information may not be released.

For adoptions that took place after August 13, 1986, the permission of the adoptive parents is unnecessary. Identifying information regarding adult biological siblings of adult adoptees may be released by a court if it is found that such information is necessary for urgent health-related purposes or if consent is provided by the adult biological sibling. 
Mo. Rev. Stat. 453.131.