Grefsen is a neighbourhood in the city of Oslo, Norway. Grefsen was a part of the municipality of Aker before the Second World War, later incorporated into Oslo. Together with Kjelsås, Grefsen then formed the borough Grefsen-Kjelsås until 1 January 2004, when they became part of the new borough of Nordre Aker. The Gjøvik Railway Line goes through the area, but Grefsen Station is actually located closer to the neighbourhood of Disen. The Kjelsås Tram Line also runs through the area. The local sports field Grefsen stadion is the home field of .