"A follow up examination of tests from pigmented skin lesions revealed 27 cases of misdiagnosis. These can be connected to a pathologist who was employed on an hourly basis as a pensioner and who is no longer working at the hospital," according to a statement on the hospital's webpage on Wednesday.
The doctor was a long term employee at the hospital until last week and the hospital was unable to rule out the possibility of more undetected cases.
The statement was issued in response to a report in the Svenska Dagbladet daily on Wednesday.
The hospital's communications director, Marielle Korend Larsson, explained that the hospital has taken steps to contact the affected patients.
"The hospital expects to be able to offer all assessment and possible treatment within a week," she wrote.
Older test samples will be examined by an independent external party spanning a period of up to five years as the doctor in question was employed at the hospital prior to drawing his pension.
The hospital has also began the compilation of a report in accordance with Lex Maria, the informal name used to refer to regulations governing the reporting of injuries or incidents in the Swedish health care system.
The hospital has also decided to open a dedicated emergency phone line for concerned patients.
Nearly 3,000 people in Sweden get malignant melanoma each year, with around 450 fatalities.
In recent years the number of cases nationally has increased by four percent. Dermatologists believe that the surge is a result of sunbathing, which became a popular pastime in 1970s and 1980s.