Stockholm District Court gave out the punishment on Tuesday morning, finding 38-year-old Martin Trenneborg guilty of kidnapping the woman. However, it found him not guilty of aggravated rape. He was also told to pay 180,000 kronor ($21,200) in damages to the victim.
Described in the media as "Sweden's Fritzl" – a reference to the Austrian father who held his daughter captive over 24 years – Trenneborg had been accused of drugging his victim by lacing stawberries and driving her to his country home while wearing a mask and fake number plates last autumn.
He had then been accused of locking the woman into what the prosecution has described as an above-ground "bunker" he had built in his yard, which resembles a garden shed from the outside.
The court said in a statement announcing the verdict that his purpose had been to keep the victim locked up to "force [her] to serve as girlfriend and future sex partner".
"The doctor planned his crime meticulously and over a long period. In addition he put the victim at serious risk by drugging her and holding her in very uncomfortable conditions in this isolated bunker," it said.
But it freed him from the rape charge he was facing, saying that it had not been proven beyond reasonable doubt that he had "carried out intercourse with the victim when she was drugged".
A bed in the bunker where the woman was held. Photo: Police
During the trial, the victim was visibly shaken, and appeared with her hands covered by black gloves and her head hidden under a scarf. Her identity has not been disclosed.
"She's not well. It's very difficult for her to face," her lawyer Jens Högström told the court.
Trenneborg has admitted to keeping her against her will, but had denied kidnapping or raping her.
"They had sexual intercourse, but that was consensual. She's a sex worker and he paid for the sex he had," his defence lawyer Mari Schaub told the AFP news agency after the verdict.
During the trial, which was mostly held behind closed doors, she said that Trenneborg was a "broken soul" and a lonely man with few friends.
"He desperately wanted a girlfriend," she told Swedish newspapers last month.
In earlier police interviews with officers the doctor said that "girlfriend might be the best term" for the woman, although he admitted she was "not a girlfriend in the ordinary sense, even I can understand that".
However the woman he locked up told police she feared she could be tortured or killed.
Detectives first became aware of the unusual plot in September 2015, after Trenneborg presented himself at a police station along with the woman, but he was not formally charged until January this year.