Madsen was last seen in the South Seaside Park area of Berkeley Township, New Jersey on June 25, 2009. She and her husband of fifty years normally reside in Clifton, New Jersey, but they were staying at their summer home in Berkeley Township when she disappeared. At 7:00 p.m., Madsen told her husband she was going for a short walk on the beach, which was about 15 yards from their home. She never returned and has never been heard from again. Her family reported her missing at 8:00 p.m. An extensive search of the area turned up no sign of her. No witnesses reported seeing her on the beach that evening, and her family stated she disliked swimming and wouldn't have gone into the water.

Madsen left behind her keys, money and identification when she disappeared. Although her Alzheimer's Disease was worsening, her family stated she knew who she was and had never gotten lost before. Her case remains unsolved.