Nurses are "propping up" the NHS by repeatedly working more hours than contracted and providing last-minute shift cover, a union has claimed.
The Royal College of Nursing (RCN) Scotland said a survey of its members found just one in 10 felt there was enough staff where they worked.
The "snapshot" survey of 200 Scottish nurses was part of a UK-wide poll.
Royal College of Nursing Scotland released the figures on the eve of its annual congress.
Almost all nurses (96%) reported working in excess of their contracted hours, with more than a quarter (27%) saying they did this every shift.
Just 11% of respondents said that staffing levels at their place of work were quite good or very good, while more than a quarter said they provided last-minute cover for absentee staff at least fortnightly.
RCN Scotland said it was worrying if some nurses felt they did not have enough staff to deliver quality care. The union warned that patient safety could be compromised as a result.
The union's director in Scotland, Theresa Fyffe, said: "The health and well-being of NHS staff is a major concern. If they become overstretched and stressed because they or colleagues are ill, there is a risk that poor practice can emerge.
"In Scotland, we are asking the next government to ensure that health boards implement the recommendations of the Boorman Review into NHS staff health and well-being.
"This is one way in which the NHS can begin to take better care of staff to allow staff to provide the standard of care they would like."
When it came to working conditions, 29% of nurses said they missed their meal time at work at least three times a week, while one in six said they rarely or never took the breaks they were entitled to.
About one in five nurses said that in the past six months they had spent a week or more at work despite feeling too ill to be there.