Adults who host underage drinking parties can be held civilly liable for injuries caused by a drunken guest, Maryland's highest court ruled unanimously on Tuesday in what one lawyer called a landmark decision.

The Court of Appeals ruled in two lawsuits brought by victims of drunken driving incidents against adults who hosted parties that led to an underage guest becoming drunk.

The court based its decision on a Maryland criminal law that makes it illegal to serve alcohol to underage people outside of immediate family or a religious service.

Judge Sally D. Adkins wrote that people under 21 are less able to make responsible decisions regarding alcohol. Part of that law "carved out that specific class for special protection against adult social hosts who knowingly and willfully allow consumption of alcoholic beverages on their property."

The decision returns two cases back to trial courts. One lawsuit was brought by Nancy Dankos, whose son, Steven Dankos, 17, was killed in 2009 in a truck crash while getting a ride home from a party at which he had consumed alcohol.

Nancy Dankos alleged that if Steven Dankos had been sober, he would not have accepted a ride in the back of a pickup from a drunken partygoer at an Ellicott City home.

The driver of that truck pleaded guilty to negligent homicide while driving under the influence in Steven Dankos' death.

Timothy F. Maloney, Dankos' attorney, called the high court's decision a landmark.

"There is a class of parents called 'cool parents,' and this decision should discourage the 'cool parents' who don't understand the harm of providing alcohol to teenagers,'' Maloney told The Daily Record in Baltimore.