Under the FMLA, an employee is entitled to take up to 12 weeks of leave from work in a 12-month period to care for a son or daughter who is an adult (18 years of age or over), if the son or daughter:

However, the FMLA and its regulations do not address whether it is relevant to the definition of "son or daughter" under the FMLA if the disability begins on or after the son or daughter turns 18 years old. (This question is irrelevant for children who are under the age of 18, because the FMLA provides parental leave rights to care for a minor child who has a serious health condition, without regard to whether the child has a disability.)

On January 14, 2013, in Administrator's Interpretation 2013-1, the Acting Deputy Administrator of the DOL's Wage and Hour Division (WHD) provided guidance on this issue. Based on the legislative and enforcement history of the FMLA, it is the Administrator's interpretation that the date of onset of the disability is irrelevant to the definition of "son or daughter" under the FMLA.

The legislative history of the FMLA recognized that:

The WHD addressed these points in several opinion letters and in the 2008 FMLA Final Rule. The 2008 Final Rule states that a child whose disability did not begin until adulthood could be considered a "son or daughter" under the FMLA. Therefore, it does not matter when the disability began.

The Administrator's Interpretation also provides guidance on the impact of the ADAAA on employees' FMLA leave rights to care for a disabled adult son or daughter. The WHD has always used the ADA's definition of disability to define an adult "son or daughter" covered under the FMLA, and the 2008 FMLA Final Rule incorporated the ADAAA's changes to the definition of disability into the FMLA regulations. When an employee requests FMLA leave to care for an adult son or daughter with a disability, the employer must consider whether the son or daughter has a disability as defined under the ADAAA. The ADAAA broadened the scope of the definition of disability under the ADA, and this definition must be construed in favor of broad coverage. For example, the ADAAA has expanded the list of major life activities affected by the disability, and if an impairment is episodic or in remission, it is a disability if, when active, it would substantially limit a major life activity.

However, even when an adult son or daughter's disability meets the requirements of the ADAAA, an employee can take leave under the FMLA to care for the son or daughter only if the:

All of these requirements must be met for a parent to receive FMLA leave to care for an adult son or daughter. For example, if an employee has an adult son with diabetes who can live on his own without assistance, the son will be considered disabled under the ADA but capable of providing daily self-care, and therefore he will not be an adult "son" under the FMLA. Therefore, if he is admitted to the hospital because of a sports-related injury that is not a disability, his parents will not be able to take FMLA leave. However, if the son loses the ability to walk because of his diabetes, and cannot bathe or dress himself, he will be considered an adult "son" under the FMLA, because he is incapable of self-care.

Finally, the Administrator's Interpretation provides clarification for parents of military service members who are wounded or injured in the course of military service. Currently, the military caregiver provision of the FMLA allows the parent of a covered service member to take up to 26 weeks of leave from work to provide care. These 26 weeks may be taken within a 12-month period, if all other requirements are met. In light of the ADAAA's expanded definition of disability, and the Interpretation's clarification that it is irrelevant, for purposes of the FMLA, when an adult "son or daughter" becomes disabled, the parent of a wounded military service member may take FMLA leave in subsequent years to provide additional care.