Four in 10 (41%) of jewellery-related claims are caused by theft, according to research.
Based on data from Churchill, accidental loss also generates the same amount of claims, while accidental damage is the reason for 18% of cases.
Rings are the most common items reported to insurers, accounting for 22% of claims. Watches come second (12%), followed by earrings (10%) and bracelets (7%).
In a separate study, based on a survey of more than 2,000 UK adults, 17% believe they own jewellery that could be considered vintage or antique. Of those, 41% confirmed their pieces are not accounted for on their home insurance policy.
Martin Scott, head of Churchill Home Insurance, said: "We urge people to regularly take the time to have their jewellery valued and make sure they are comprehensively insured on a policy that protects the full value."
The survey also shows 16% of respondents do not have any type of home insurance, "offering no protection for their crown jewels". Of those who are insured, a third (34%) do not know if their policy has a single item limit.
"It is important to consider if you have an item which exceeds the policy limit and follow the procedure necessary to insure that item," Scott said.
"For many, the impact of under-insurance is only realised when it's too late, but this is preventable."
Most common reason for claiming
Theft - 41%
Accidental loss - 41%
Accidental damage - 18%
Most common jewellery item claimed
Ring - 22%
Watch - 12%
Earrings - 10%
Bracelet - 7%