Costs of informal care account for a significant component of total societal costs for many chronic and disabling illnesses. Yet, costs associated with the provision of informal care is seldom included in economic evaluations of new health technologies, increasing the risk of suboptimal decisions on the allocation of resources from the perspective of society. Our objective was to propose a standardized questionnaire for the measurement, valuation, and estimation of caregiver indirect (productivity) and informal care costs as separate mutually exclusive subsets of total costs in cost-of-illness studies and as an input to economic evaluations from the societal perspective. We developed a questionnaire for data collection and step-by-step analysis procedures for resource valuation and cost estimation. Data concerning absenteeism from work and time devoted to informal care were recorded using the recall method. Indirect (productivity) and paid informal care costs were valued and estimated according to the human-capital approach as the loss of production. Unpaid informal care costs were valued and estimated as the loss of leisure time quantified using the opportunity cost and proxy good method. The new questionnaire, titled the Caregiver Indirect and Informal Care Cost Assessment Questionnaire, contains 13 questions regarding caregiver current and previous work status, productivity, and the provision of informal care (stratified by time devoted to household activities, personal care, practical support, and emotional support). The proposed questionnaire should be helpful to inform the design, implementation, and execution of future cost-of-illness studies and economic evaluations from the perspective of society.