Cigarette smoking can become an issue in a custody case even where the smoker is not the parent of the child. Parties have raised ETS as an issue when stepparents, paramours and other persons who smoke come into regular contact with the child. In these cases, the focus is generally on the harm to the child and the custodial parent's responsibility to prevent that harm.

Several decisions have cited smoking by other family members in making a decision on custody. In Gilbert the court changed custody notwithstanding the preference of the child "in view of the serious and continuous hazard to his physical health while his mother and stepfather continue to smoke." The West Virginia Supreme Court found that as both the custodial parent and other "family members" smoke, the court could restrict the entire family's smoking around the child.

There is no reported case in which the issue of custody was decided solely due to ETS caused by a party other than the natural parent. However, as third parties do not have the discretion afforded parents in raising their children, it would seem that courts will have less tolerance to exposing children to ETS caused by these individuals. This will place an added burden on custodial parents to ensure that persons who they bring into the household do not smoke in the presence of the child.