"This means a lot to us. Unfortunately, it's taken a very long time, which means that research has suffered," Gustaf Edgren from Karolinska Institutet told the TT news agency following the ruling.
Last year, researchers at Karolinska near Stockholm linked around 1,000 donors in northern Sweden to recipients who later developed respiratory distress.
Numerically, the donors could each be related to 14 cases of transfusion-related acute lung damage (TRALI).
Despite repeated requests for access to the registry, county officials and local courts struck down their appeals.
Citing privacy concerns, the Sundsvall District Court denied them access to the names of the donors. Researchers have since appealed the decision, arguing that no donors would be put at risk as Karolinska itself strictly safeguards privacy and data integrity.
Researchers had said they wanted to interview donors about their medical history to examine what they said was probably a previously unknown "auto-immune response" linked to the lung condition.
"You have to assume that a blood donor, who has done a good deed for society and for other people, would find it very odd that we, out of respect to the donor, would put our heads in the sand and let this continue,” Karolinska wrote in its appeal.
On Monday, an administrative appeals court granted the researchers access.
Should their plans now go ahead, they will further analyze the donor's blood as well as go through their medical history in detail.
The magazine Vårdfokus reported that half of the patients who developed TRALI died from it. Healthcare professionals believe that this reaction to blood transfusions accounts for most transfusion-related deaths, but as knowledge about it is scant, occurrence is likely under-reported.
"TRALI is now among the three leading causes of transfusion-related fatalities along with ABO incompatibility and bacterial contamination," states the website of the Canadian Blood Services.