Nine out of 10 senior doctors and dentists in New Zealand's public hospitals say have gone to work when too unwell to perform to usual standards.

The finding comes in a study by the Association of Salaried Medical Specialists and Otago University, and published in the NZ Medical Journal.

The authors say this suggests that doctors and dentists are forcing themselves to go into work because of pressure to keep the public health system functioning.

The study aimed to estimate the rates of presenteeism - working when too unwell, fatigued or stressed - among New Zealand's senior medical workforce.

It involved a survey that 1806 of 3740 potential participants completed.

Presenteeism over the past two years was reported by 88 per cent of respondents, with women and younger doctors having the highest rates.

Reasons given included difficulties in getting short-term sickness cover and concern over the impact of sick leave on patients.

The report says the findings suggest that presenteeism behaviour is common, well recognised and an issue of concern.

They also suggest that senior doctors are keenly aware of the pressures on the public health system and how taking sick leave can add to the workloads of their colleagues.

"Conversely, however, the high rates of continuing to work while unwell and while infectious suggest a worrying picture where the potential for further risk of harm to both practitioner and patient alike is considerable," the authors said.

"Importantly, presenteeism is unlikely to decrease if individuals are operating in environments where working through illness is viewed as 'normal' or, at worst, 'necessary' behaviour."

Researcher Charlotte Chambers from the Association of Salaried Medical Specialists said doctors face a difficult choice.

"Do I turn up to work today when I'm suffering from a head cold, or do I stay home but potentially prevent my patients from being seen."