|This article centers around Jason DiLaurentis, a book character. For another version check out Jason DiLaurentis, a TV character.|
|“||My sister was like that. She knew everyone's precise button to push.||”|
Jason DiLaurentis is the older brother of the twins — Alison and Courtney. Though his younger sisters share the same father as Spencer and Melissa Hastings, note that he is not the half-brother of the Hastings girls or related to them in any way as they share no biological parents. Before the DiLaurentises moved to Rosewood their last name was Day-DiLaurentis, they changed it due to their secret daughter Courtney.
Jason is an attractive young man, with blonde hair and brooding eyes. He is the only child to be produced from the DiLaurentis marriage, as Courtney and Alison were produced from an affair Jessica DiLaurentis had with Peter Hastings.
Jason was in the same class year as Melissa and Ian Thomas, along with good friend Darren Wilden. He had a crush on Melissa in high school but she didn't return his feelings. They had a brief fling and Melissa moved on to date Ian. Jason was a bit troubled in his high school days, dealing with the chaos produced by his sisters' animosity towards each other and his parents' tense marriage. He hung out with Darren often, who was a known troublemaker back in the day. He took Alison's time capsule flag from Courtney and gave it to Aria Montgomery. It seems that Jason was unaware of the switch between his sisters. He used to visit Courtney quite often at the Radley Institute; when Alison was shunted off to the Preserve at Addison-Stevens, he eventually stopped visiting because he was swamped with schoolwork and couldn't make the time. He occasionally got calls from her while he was in school, aggravating him and contributing to his moodiness. Jason was in Costa Rica to teach adventure kayaking when Alison killed Courtney during the night of the sleepover.
The DiLaurentises eventually moved out of Rosewood after "Ali's" disappearance, and Jason attended Yale University. Eventually he transferred to a more local Ivy, the University of Pennsylvania and moved into his parents' new home in Yarmouth in order to help them out during Ian's trial. He and Aria randomly met at the train station; Aria had a crush on him in 7th grade and was flattered that he remembered her name. He seemed to like her as well, telling her she was the only friend of "Ali's" that had "substance". She and Jason went on a few outings together, but she noted his very odd behavior. When she first met up with him, he freaked out when a story claiming Ian Thomas was not dead appeared on the monitor. He also flipped out when Aria invited him to a party at the Radley, where Courtney once stayed. Emily Fields also had some encounters with Jason, but none of them were pleasant. He frightened her and she honestly believed he was involved in "Ali's" death at one point.
More was discovered about Jason's mysterious persona when Aria received a fake email from him inviting her to his apartment in Yarmouth. While being chased by a Rottweiler on the property, she is forced to break into his apartment for safety. She discovers his old yearbook while inside and finds that not only were he and Darren best friends, but they also strongly disliked Ian. He arrives at his apartment to find her riffling through his yearbook and becomes truly angered. Later she and Emily are at the party in the Radley and find guestbooks with his signature under many dates. They also learn the Radley was a mental institution before it was closed down and renovated. The girls believe he is insane and after the woods behind Spencer's barn is set on fire, they believe he and Darren worked to pull off the crime. In Heartless, Aria accuses him with what she knows, but he is astonished and tells her that she's completely wrong. Only in Wanted does she completely understand what he meant by that. While "Courtney" is hanging out with Emily, she notices Jason staring at them with an infuriated expression. When the truth about who was really killed that summer night finally comes out, Jason and his parents flee the area. There is no indication of whether Jason knew his sisters had switched before Alison tried to kill her sister's friends in the Poconos.