This study values informal care for disabled stroke survivors in Thailand. It applies the conventional recommended opportunity cost method to value informal care in monetary terms. Data were collected by means of face-to-face interviews conducted during 2006. The sample consisted of 101 disabled persons who had suffered a stroke at least six months prior to the interview, and who had a functional status score of less than 95 as measured by the Barthel Index. Average monthly time spent on informal care was 94.6 hours, and the major source of opportunity cost was forgone unpaid work (43.5%). The average monthly monetary value of informal care was 4642.6 baht, based on 2006 prices. This study shows that providing informal care involves a substantial opportunity cost, implying a hidden value to Thai society.