The police and medical services were called just before 8:30 p.m. to a home in Haninge, south of Stockholm. A man in his 30s is suspected of stabbing a man in his 50s, who was then taken by helicopter to hospital. The extent of the injuries is unknown.
The men have, according to police spokesman Daniel Wikdahl, a family relationship.
There were a number of other people in the home who were related.
A technical investigation and interrogation will be initiated.
The police have arrested the suspected perpetrator.
