Voluntary benefits are those for which employees pay the full cost.

The survey of 138 companies found that 75 percent offer employees supplemental life insurance, such as the ability to increase the amount of coverage or to obtain coverage for a spouse or child. Forty-six percent of companies offer the next most common voluntary benefit, disability insurance, and 35 percent offer employees vision insurance.

Employees showed a marked interest in vision coverage, which was taken up, on average, by 59 percent of workers who were offered it. Just 38 percent of employees signed up for disability insurance and 36 percent took advantage of supplemental life insurance.

Erin O’Connor, practice leader for human resources at Cammack LaRhette, said the availability of long-term care insurance was higher than expected, with 26 percent of companies offering it and an average of 8.5 percent of workers participating.

Less common voluntary benefits include critical illness insurance, cancer coverage, legal assistance, pet insurance and identity-theft insurance, according to the survey.

Filed by Susan Kelly of Financial Week, a sister publication of Workforce Management. To comment, e-mail editors@workforce.com.