Laya Healthcare is to push up prices by an average of 4% on more than half of its policies.
The increase will take effect from September 1 and affect 59 different schemes.
The company has blamed the hike on the growth in the volume and costs of medical claims it has received in the past year - citing an 18% increase in the number of claims, and a 15% increase in the cost of those claims.
It follows price increases by competitors Aviva and GloHealth earlier this year.
It is understood that price increases will range from 2% - 9%, and the company's top-end plans are least likely to be affected.
"We are acutely conscious of the impact this adjustment will have on some of our members, and we have tried to minimise the impact across our schemes," Managing Director Dónal Clancy said in a statement.
"While better practices, high-spec technology and improved treatments are all translating into better patient outcomes, they are driving medical costs higher; which in turn has a negative impact on premiums."
At the same time as the price increases, children's rates will be decreased on a number of schemes, and some schemes will see the excess for day cases substantially reduced.
Health insurance analyst Dermot Goode said that the careful consumer can avoid price rises.
"Any Laya member that is affected by this price increase From September onwards, the good news is that if they look more closely, they should be able to find an equivalent plan to what they have and miss the price increase completely," he said.
"They may not even have to change insurance companies.
"So really the message is - Don't accept these price increases. Look for the lower-cost equivalents, which are there, and in many cases you'll be able to reduce your costs."