Including informal care in economic evaluations is increasingly advocated but problematic. We investigated three well-known concerns regarding contingent valuation (CV): (1) the item non-response of CV values, (2) the sensitivity of CV values to the individual circumstances of caring, and (3) the choice of valuation method by comparing willingness-to-pay (WTP) and willingness-to-accept (WTA) values for a hypothetical marginal change in hours of informal care currently provided. The study sample consisted of 1453 caregivers and 787 care recipients. Of the caregivers, 603 caregivers (41.5%) provided both WTP and WTA values, 983 (67.7%) provided at least one. Determinants of non-response were dependent on the valuation method; primary determinants were education and satisfaction with amount of informal care provided. Caregivers' mean WTP (WTA) for reducing (increasing) informal care by 1 h was €9.13 (10.52). Care recipients' mean WTA (WTP) for reducing (increasing) informal care by 1 h was €8.88 (€6.85). Values were associated with a variety of characteristics of the caregiving situation; explanatory variables differed between WTP and WTA valuations. The differences between WTP and WTA valuations were small. Based on sensitivity CV appears to be a useful method to value informal care for use in economic evalations, non-response, however, remains a matter of concern. Copyright © 2009 John Wiley & Sons, Ltd.