Police rushed to the scene in Malmö late on Sunday evening after the alarm was raised. The man was found with grievous stab wounds to his neck and was taken to hospital where he was pronounced dead.
A woman, who was in the apartment, was arrested for attempted murder.
Local police said that the woman didn't have a prior criminal record. Despite knocking on several doors in the apartment complex they were unable to find any witnesses to the incident.
Neighbours in the area reported that they didn't hear any disturbances throughout the evening. One resident told the TT news agency that they had heard loud music coming from the apartment earlier in the evening, but police were unable to confirm this.
The authorities have since cordoned off the scene and conducted a technical examination. By Monday morning the examination was complete reported the Sydsvenskan newspaper.
"We don't know yet how the man got the stab wounds to his neck. We have not found a murder weapon," Hans Nilsson of the Skåne police told TT.
Neither the suspect nor the deceased man had their names written on the apartment door and it hasn't been established whether they were known to one another.
Police added that the man who died was not a Swedish citizen and was known to them for having a criminal past. However, they stated any such offences happened quite a long time ago.
His body has since been transferred to nearby Lund where it will be examined by the coroner.
The suspected woman is due to be examined by a doctor and be questioned by the police throughout Monday.