Pfizer's annual Health & Science Index found that one in five people are worried that may have missed a diagnosis and treatment during the pandemic.
Almost 50% of respondents confessed to either cancelling or missing scheduled medical appointments.
Over-65s were the group with the most cancellations at 28%.
11% of adults said they declined seeking treatment despite feeling sick.
This year's survey does however show that people are feeling more confident now about visiting a hospital. 18% said they would not visit a hospital, down from 27% last year.
43% of those surveyed said the pandemic had negative implications on their health, citing mental health, weight gain and lack of exercise.
The serious illness respondents are most worried about being affected by in the future is cancer, with 50% expressing concern. 40% are concerned with heart disease.
"Covid-19 has presented many health system challenges which have made it more difficult for the public to access non-Covid care," said Irish Cancer Society director of advocacy and external affairs Rachel Morrogh. "The findings underscore the importance that if anyone is worried about missing an appointment or if they have not sought medical advice yet, to make an appointment with their GP or clinician as soon as possible."
Irish Heart Foundation head of advocacy Chris Macey urged anyone who fears they may have missed a diagnosis "to make that appointment that they have been putting off today and not wait until it’s too late" and said "people should feel confident that it is safe to visit their GP or clinician in person."
