Ahmad Subhi al-Kahlout's relatives say they were informed that he is being held at al-Majdal prison in southern Israel. It is unclear why he was detained.
An Israeli security official could not be reached for comment.
Palestinians granted permission to enter Israel must pass through the Erez crossing. A number of sick Palestinians entering Israel for medical treatment have been detained at the terminal.
In January, Bassam Rehan, 25, from Jabaliya refugee camp, was arrested at the Erez crossing in northern Gaza, witnesses told Ma'an. He was en route to Israel for medical treatment.