OBJECTIVES: Many individuals with long-term care needs rely on informal care to support them in their daily living.  Although public authorities tend to see informal care as free, caring imposes significant costs on caregivers. However, measuring and valuing informal care remains a challenge partly due to the absence of clear guidelines on the topic and partly due to the lack of consensus among economists on the best methods to use. This review describes the methods used to measure and monetarily value informal care and discusses their advantages and limitations. METHODS: Review of: 1) the methods available to measure time; 2) methods available to value informal care time; and 3) application in published economic evaluations. RESULTS: Only the diary and the recall methods have been used in cost-effectiveness analysis, although direct observation and experience sampling may provide more accurate estimates of time use. The traditional methods to value time are the opportunity cost, proxy good and contingent valuation methods. Recently, the well-being method and applications of conjoint analysis to informal care have been developed. The value of informal care varies widely depending on the methods used. CONCLUSIONS: Informal care should not be viewed as costless or free since the time inputs into informal care generate costs borne by the caregiver and society as a whole. Failure to consider informal care may affect reimbursement decisions and shift costs to patients and their families. The monetary value of informal care can be estimated using existing methods. The clear advantage of using monetary methods is that results can potentially be included in cost side of any type of economic evaluations. However, different methods give different answers both in terms of time-use data and value of informal care. Clear guidelines are needed on the preferred methods to measure and value informal care time.