Brundtland told broadcaster NRK that she experienced sexual harassment by an assistant physician ten years her senior.
Former PM Brundtland, who led Norway's government during three separate spells in the 1980s and ‘90s, worked part time in a hospital when she was a medicine student in the 1960s.
In an interview for television, she told NRK that she experienced sexual harassment during this time.
The senior colleague entered a room in which Brundtland was working on an analysis of urine samples and began to tickle her on the ear and neck.
The man was married with children, she said.
The former PM continued by saying that she felt the best thing she could do was to pretend she hadn't noticed the advance.
“I didn't move, and just sat frozen and continued with the urine tests. When he realised it was not making an impression on me, he walked out of the door,” she told NRK.
Brundtland worked as an assistant consultant in Oslo before beginning her political career. Her spells as prime minister add up to over ten years at the head of government, and she also became known as ‘the mother of the nation' (landsmoderen in Norwegian) following retirement.
Norway, like many other countries, has seen increasing numbers of women go public with their experiences of sexual harassment in the wake of the Harvey Weinstein scandal and subsequent #metoo social media campaign.
Earlier this week, 1,001 artists in the country denounced rape, assault and harassment in manifestos published by the Norwegian media.