Adult dependents are eligible for continuation of coverage if they become ineligible as an adult dependent - for instance, if they turn age 25 or prior to age 25 if there is a qualifying event that affects their eligibility (i.e. the employee terminates). The duration of the continuation of coverage - 18 or 36 months - is based on what the qualifying event is. 

For example, if an adult dependent becomes ineligible because the parent (subscriber) terminates employment, then the adult dependent would be eligible for 18 months of continuation coverage. If the adult dependent becomes ineligible because he or she turned age 25, he or she would be eligible for 36 months of continuation coverage.